Use base_ref and head_ref given commit history

Author: Happypig375

.github/workflows/Label.yml

@@ -4,15 +4,17 @@ on: [pull_request]
 jobs:
   Label:
     runs-on: windows-latest
+    permissions:
+      pull-requests: write # allow adding a label to this pull request
     steps:
     - uses: actions/checkout@v6
       with:
         submodules: recursive
-        fetch-depth: 0 # fetch all commit history across all branches and tags
+        fetch-depth: 0 # fetch all commit history across all branches and tags, instead of only one commit by default
     - name: If there are changes in PublicApi.Shipped.txt, fail the workflow
       if: github.head_ref != 'action/ship-publicapi' # Same branch name specified in Release.yml
       run: |
-        $changes = git diff --numstat --shortstat origin/${{ github.base_ref }}...HEAD -- '**/PublicApi.Shipped.txt'
+        $changes = git diff --numstat --shortstat ${{ github.base_ref }}...${{ github.head_ref }} -- '**/PublicApi.Shipped.txt'
         Write-Output "$changes"
         if ($changes) {
           Write-Error "Changes detected in PublicApi.Shipped.txt files. Public API changes must be shipped through the release process, not in regular pull requests."
@@ -21,15 +23,13 @@ jobs:
       shell: pwsh
     - name: Label based on PublicApi.Unshipped.txt
       run: |
-        git fetch origin ${{ github.base_ref }}
-        
         # Determine the appropriate label (Sync these labels with release-drafter.yml)
         if ("${{ github.ref }}" -eq "action/ship-publicapi") { # Same branch name specified in Release.yml
           $labels = @('Type/Housekeeping')
           Write-Output "This is a ship-publicapi PR, labeling as Type/Maintenance"
         } else {
           # For regular PRs, check for API changes
-          $changes = git diff origin/${{ github.base_ref }}...HEAD -- '**/PublicApi.Unshipped.txt'
+          $changes = git diff ${{ github.base_ref }}...${{ github.head_ref }} -- '**/PublicApi.Unshipped.txt'
           Write-Output "$changes"
           
           if ($changes) {