fix: if we want to allow pre-existing git checkout state, we must read its commit hash (#15)

The action allows updates to the local git clone prior to it running,
but it ignores them.

---------

Co-authored-by: Maarten Zuidhoorn <[email protected]>

Author: naugtur

action.yml

@@ -61,6 +61,13 @@ runs:
         fetch-depth: ${{ inputs.fetch-depth }}
         ref: ${{ inputs.ref }}
 
+    # Get the commit hash of the checked out commit regardless of whether it
+    # was checked out in the previous step or existed before.
+    - name: Get commit hash
+      id: get-commit-hash
+      run: echo "actual-commit-hash=$(git rev-parse HEAD)" >> "$GITHUB_OUTPUT"
+      shell: bash
+
     - run: corepack enable
       shell: bash
 
@@ -72,7 +79,7 @@ runs:
       uses: actions/cache/restore@v4
       with:
         path: ./node_modules
-        key: node-modules-${{ github.sha }}
+        key: node-modules-${{ steps.get-commit-hash.outputs.actual-commit-hash }}
 
     - name: Set up Node.js
       uses: actions/setup-node@v4
@@ -121,4 +128,4 @@ runs:
       uses: actions/cache/save@v4
       with:
         path: ./node_modules
-        key: node-modules-${{ github.sha }}
+        key: node-modules-${{ steps.get-commit-hash.outputs.actual-commit-hash }}