build: update ref handling in workflow files for improved pull request support

Author: roboticswithjulia

.github/workflows/rust-minimal.yml

@@ -39,7 +39,7 @@ jobs:
       with:
         persist-credentials: false # otherwise, the token used is the GITHUB_TOKEN, instead of your personal token
         fetch-depth: 0 # otherwise, you will failed to push refs to dest repo
-        ref: ${{ github.event.pull_request.head.ref || github.ref }}
+        ref: ${{ github.head_ref }}
 
     - uses: technology-studio-forks/markdown-embed-code@main
       with:

.github/workflows/rust-stable.yml

@@ -39,7 +39,7 @@ jobs:
       with:
         persist-credentials: false # otherwise, the token used is the GITHUB_TOKEN, instead of your personal token
         fetch-depth: 0 # otherwise, you will failed to push refs to dest repo
-        ref: ${{ github.event.pull_request.head.ref || github.ref }}
+        ref: ${{ github.head_ref }}
 
     - uses: technology-studio-forks/markdown-embed-code@main
       with: