diff --git a/.github/actions/setup/directories/action.yml b/.github/actions/setup/directories/action.yml
index 598096ef3a46d2..e91787cc409446 100644
--- a/.github/actions/setup/directories/action.yml
+++ b/.github/actions/setup/directories/action.yml
@@ -135,9 +135,21 @@ runs:
 
     - if: inputs.dummy-files == 'true'
       shell: bash
+      id: dummy-files
       working-directory: ${{ inputs.builddir }}
       run: |
         : Create dummy files in build dir
-        for basename in {a..z} {A..Z} {0..9} foo bar test zzz; do
-          echo > ${basename}.rb "raise %(do not load ${basename}.rb)"
+        set {{a..z},{A..Z},{0..9},foo,bar,test,zzz}.rb
+        for file; do \
+          echo > $file "raise 'do not load $file'"; \
         done
+        # drop {a..z}.rb if case-insensitive filesystem
+        grep -F A.rb a.rb > /dev/null && set "${@:27}"
+        echo files="$*" >> $GITHUB_OUTPUT
+
+    - if: steps.dummy-files.outcome == 'success'
+      uses: gacts/run-and-post-run@674528335da98a7afc80915ff2b4b860a0b3553a # v1.4.0
+      with:
+        working-directory: ${{ inputs.builddir }}
+        post:
+          rm ${{ steps.dummy-files.outputs.files }}