chore: s/GITHUB_*/FORGEJO_*/ & s/github./forge./ (#776)

Reviewed-on: https://code.forgejo.org/forgejo/end-to-end/pulls/776
Reviewed-by: Michael Kriese <michael.kriese@gmx.de>
Co-authored-by: Earl Warren <contact@earl-warren.org>
Co-committed-by: Earl Warren <contact@earl-warren.org>

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

@@ -23,7 +23,7 @@ jobs:
         if: ${{ env.KEY1 == 'nogood' }}
       - name: if does not skip
         id: conditional
-        run: echo 'check=good' >> $GITHUB_OUTPUT
+        run: echo 'check=good' >> $FORGEJO_OUTPUT
         if: env.KEY1 == 'value1'
       - name: verify if did not skip
         run: test ${{ steps.conditional.outputs.check }} = good