add 5507 regression test in linux

Author: Arya Irani

.github/workflows/ci.yaml

@@ -273,6 +273,10 @@ jobs:
           ${{env.transcripts}}
           # Fail if any transcripts cause git diffs.
           git diff --ignore-cr-at-eol --exit-code unison-src/transcripts
+      - name: shell-based regression tests
+        if: steps.cache-transcript-test-results.outputs.cache-hit != 'true' && runner.os == 'linux'
+        run: |
+          unison-src/tests/fix5507.sh ${{env.ucm}}
       - name: docs.to-html
         if: steps.cache-transcript-test-results.outputs.cache-hit != 'true'
         run: |