Add shell: bash to build actions

Author: joshuanianji

.github/actions/build-base-img/action.yml

@@ -44,6 +44,7 @@ runs:
         else
           echo "cache-to=" >> $GITHUB_OUTPUT
         fi
+      shell: bash
 
     - name: Build Base (versioned)
       uses: docker/build-push-action@v5

.github/actions/build-devcontainer-img/action.yml

@@ -51,6 +51,7 @@ runs:
         else
           echo "cache-to=" >> $GITHUB_OUTPUT
         fi
+      shell: bash
 
     - name: Build Devcontainer (versioned)
       if: ${{ inputs.idris-lsp-version != 'latest' }}