Save CAPI extensions cache not-cached master only

Author: nobu

.github/actions/capiext/action.yml

@@ -35,8 +35,8 @@ runs:
         echo DLEXT=$DLEXT >> $GITHUB_OUTPUT
       working-directory: ${{ inputs.builddir }}
 
-    - name: CAPI extensions cache
-      uses: actions/cache@0400d5f644dc74513175e3cd8d07132dd4860809 # v4.2.4
+    - name: Restore previous CAPI extensions
+      uses: actions/cache/restore@0400d5f644dc74513175e3cd8d07132dd4860809 # v4.2.4
       id: cache
       with:
         path: ${{ inputs.builddir }}/spec/ruby/optional/capi/ext/
@@ -50,11 +50,24 @@ runs:
         touch spec/ruby/optional/capi/ext/*.$DLEXT
         [ ! -f spec/ruby/optional/capi/ext/\*.$DLEXT ]
         ${{ inputs.make }} SPECOPTS=optional/capi test-spec
+        rm -f spec/ruby/optional/capi/ext/*.c
       env:
         DLEXT: ${{ steps.config.outputs.DLEXT }}
       working-directory: ${{ inputs.builddir }}
       if: ${{ steps.cache.outputs.cache-hit }}
 
+    - name: Save CAPI extensions
+      uses: actions/cache/save@0400d5f644dc74513175e3cd8d07132dd4860809 # v4.2.4
+      with:
+        path: ${{ inputs.builddir }}/spec/ruby/optional/capi/ext/
+        key: ${{ steps.config.outputs.key }}
+      if: >-
+        ${{true
+        && steps.cache.outcome == 'success'
+        && ! steps.cache.outputs.cache-hit
+        && github.ref_name == 'master'
+        }}
+
     - shell: bash
       run: |
         echo "::error::Change from ${prev} detected; bump up ABI version"