test: add reusable workflow expansion test for outputs (#1322)

In the "reusable workflow expansion" case (that is, when `runs-on` is not provided), this PR adds tests for `on.workflow_call.outputs`, and expands the test case to have two layers of reusable workflows to cover quirky behaviours that were discovered during manual testing.

Manual invocation successful:
![image](/attachments/0406a783-4ef6-4854-a376-421ccc86b854)

Reviewed-on: https://code.forgejo.org/forgejo/end-to-end/pulls/1322
Co-authored-by: Mathieu Fenniak <mathieu@fenniak.net>
Co-committed-by: Mathieu Fenniak <mathieu@fenniak.net>

actions/example-workflow-call-expansion/.forgejo/workflows/reusable-layer-1.yml

@@ -0,0 +1,49 @@
+on:
+  workflow_call:
+    outputs:
+      output1:
+        value: ${{ jobs.callee-1.outputs.job-output }}
+      output2:
+        value: ${{ jobs.callee-2.outputs.job-output }}
+      output3:
+        value: ${{ jobs.layer-2.outputs.output3 }}
+      output4:
+        value: ${{ jobs.layer-2.outputs.output4 }}
+
+jobs:
+  callee-1:
+    runs-on: docker
+    outputs:
+      job-output: callee-1-output
+    container:
+      image: data.forgejo.org/oci/node:22-bookworm
+      volumes:
+        - /srv/example:/srv/example
+    steps:
+      - name: indicate callee-1 hit
+        run: touch /srv/example/callee-1
+
+  layer-2:
+    uses: ./.forgejo/workflows/reusable-layer-2.yml
+
+  callee-2:
+    needs: [callee-1, layer-2]
+    runs-on: docker
+    outputs:
+      job-output: callee-2-output
+    container:
+      image: data.forgejo.org/oci/node:22-bookworm
+      volumes:
+        - /srv/example:/srv/example
+    steps:
+      - name: verify callee-1 completed
+        run: |
+          set -x
+          test -f /srv/example/callee-1
+      - name: verify layer-2 completed
+        run: |
+          set -x
+          test -f /srv/example/callee-3
+          test -f /srv/example/callee-4
+      - name: indicate callee-2 hit
+        run: touch /srv/example/callee-2

actions/example-workflow-call-expansion/.forgejo/workflows/reusable-layer-2.yml

@@ -0,0 +1,37 @@
+on:
+  workflow_call:
+    outputs:
+      output3:
+        value: ${{ jobs.callee-3.outputs.job-output }}
+      output4:
+        value: ${{ jobs.callee-4.outputs.job-output }}
+
+jobs:
+  callee-3:
+    runs-on: docker
+    outputs:
+      job-output: callee-3-output
+    container:
+      image: data.forgejo.org/oci/node:22-bookworm
+      volumes:
+        - /srv/example:/srv/example
+    steps:
+      - name: indicate callee-3 hit
+        run: touch /srv/example/callee-3
+
+  callee-4:
+    needs: callee-3
+    runs-on: docker
+    outputs:
+      job-output: callee-4-output
+    container:
+      image: data.forgejo.org/oci/node:22-bookworm
+      volumes:
+        - /srv/example:/srv/example
+    steps:
+      - name: verify callee-3 completed
+        run: |
+          set -x
+          test -f /srv/example/callee-3
+      - name: indicate callee-4 hit
+        run: touch /srv/example/callee-4

actions/example-workflow-call-expansion/.forgejo/workflows/reusable.yml

@@ -1,28 +0,0 @@
-on:
-  workflow_call:
-
-jobs:
-  callee-1:
-    runs-on: docker
-    container:
-      image: data.forgejo.org/oci/node:22-bookworm
-      volumes:
-        - /srv/example:/srv/example
-    steps:
-      - name: indicate callee-1 hit
-        run: touch /srv/example/callee-1
-
-  callee-2:
-    needs: callee-1
-    runs-on: docker
-    container:
-      image: data.forgejo.org/oci/node:22-bookworm
-      volumes:
-        - /srv/example:/srv/example
-    steps:
-      - name: verify callee-1 completed
-        run: |
-          set -x
-          test -f /srv/example/callee-1
-      - name: indicate callee-2 hit
-        run: touch /srv/example/callee-2

actions/example-workflow-call-expansion/.forgejo/workflows/test.yml

@@ -2,19 +2,28 @@ on:
   push:
 
 jobs:
-  caller:
-    uses: ./.forgejo/workflows/reusable.yml
+  layer-1:
+    uses: ./.forgejo/workflows/reusable-layer-1.yml
 
   verify:
-    needs: [caller]
+    needs: [layer-1]
     runs-on: docker
     container:
       image: data.forgejo.org/oci/node:22-bookworm
       volumes:
         - /srv/example:/srv/example
     steps:
-      - name: verify callee-1 & callee-2 completed
+      - name: verify callee-[0-4] completed
         run: |
           set -x
           test -f /srv/example/callee-1
           test -f /srv/example/callee-2
+          test -f /srv/example/callee-3
+          test -f /srv/example/callee-4
+      - name: verify workflow outputs
+        run: |
+          set -x
+          test "callee-1-output" = "${{ needs.layer-1.outputs.output1 }}"
+          test "callee-2-output" = "${{ needs.layer-1.outputs.output2 }}"
+          test "callee-3-output" = "${{ needs.layer-1.outputs.output3 }}"
+          test "callee-4-output" = "${{ needs.layer-1.outputs.output4 }}"