actions: shell: assert shell behavior (#788)

Refs https://code.forgejo.org/forgejo/runner/issues/150

Reviewed-on: https://code.forgejo.org/forgejo/end-to-end/pulls/788
Co-authored-by: Earl Warren <contact@earl-warren.org>
Co-committed-by: Earl Warren <contact@earl-warren.org>

actions/example-shell/.forgejo/workflows/test.yml

@@ -0,0 +1,78 @@
+on: [push]
+
+env:
+    ASSERT_SHELL: 'set -x ; readlink /proc/$$/exe ; readlink /proc/$$/exe | grep '
+
+jobs:
+  default:
+    # docker:docker://code.forgejo.org/oci/node:22-bookworm
+    runs-on: docker
+    steps:
+      - name: default is bash
+        run: |
+            ${{ env.ASSERT_SHELL }} /bash
+
+  defaults-run:
+    needs: [default]
+    # alpine:docker://code.forgejo.org/oci/alpine:latest
+    runs-on: alpine
+    defaults:
+        run:
+            shell: sh
+    steps:
+      - name: default is sh which is an alias for busybox in alpine
+        run: |
+            ${{ env.ASSERT_SHELL }} /busybox
+
+  alpine:
+    needs: [defaults-run]
+    runs-on: docker
+    container:
+      image: code.forgejo.org/oci/alpine:latest
+    steps:
+      - name: default is sh which is an alias for busybox in alpine
+        run: |
+            ${{ env.ASSERT_SHELL }} /busybox
+
+  python:
+    needs: [alpine]
+    runs-on: docker
+    container:
+      image: code.forgejo.org/oci/python:slim
+    steps:
+      - name: python => python {0}
+        shell: python
+        run: |
+            print("something")
+
+  other:
+    needs: [python]
+    runs-on: docker
+    container:
+      image: code.forgejo.org/oci/node:22-bookworm
+    steps:
+      - name: default is sh which is an alias for dash in bookworm
+        run: |
+            ${{ env.ASSERT_SHELL }} /dash
+
+      - name: bash => bash --noprofile --norc -e -o pipefail {0}
+        shell: bash
+        run: |
+            ${{ env.ASSERT_SHELL }} /bash
+            shopt -o
+            shopt -o | grep --quiet 'pipefail.*on'
+
+      - name: sh => sh -e {0}
+        shell: sh
+        run: |
+            ${{ env.ASSERT_SHELL }} /dash
+
+      - name: node => node {0}
+        shell: node
+        run: |
+            console.log("something")
+
+      - name: dash -e {0}
+        shell: dash -e {0}
+        run: |
+            ${{ env.ASSERT_SHELL }} /dash