fix: add shell property (#5)

Author: pranc1ngpegasus

action.yml

@@ -8,7 +8,8 @@ inputs:
 runs:
   using: "composite"
   steps:
-    - run: |
+    - shell: bash
+      run: |
         gh extension install actions/gh-actions-cache
 
         mergedPRNumbers=$(gh pr list --state merged --json number | jq .[].number)