Use bash shell when using here-strings (scala#21817)

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[positive](https://github.com/WojciechMazur/dotty/actions/runs/11416876799/job/31768568868)
test in scala#21810 also uses `bash` instead of `sh`

Closes scala#21815

Author: hamzaremmal

.github/workflows/ci.yaml

@@ -664,6 +664,7 @@ jobs:
           echo "THISBUILD_VERSION=$ver" >> $GITHUB_ENV
 
       - name: Check is version matching pattern
+        shell: bash
         run: |
           if ! grep -Eo "3\.[0-9]+\.[0-9]+-RC[0-9]+-bin-[0-9]{8}-[a-zA-Z0-9]{7}-NIGHTLY" <<< "${{ env.THISBUILD_VERSION }}"; then
             echo "Version used by compiler to publish nightly release does not match expected pattern"