github actions: Fix process-pull-request for forks

The process-pull-request workflow was failing for pull requests
originating from forked repositories. The previous implementation
incorrectly assumed the pull request branch existed on the base repository.

This commit corrects the workflow to ensure the pull request branch
is checked out from the correct source repository, while the base
branch is fetched from the target repository.

Author: bmastbergen

.github/workflows/process-git-request.rb

@@ -22,7 +22,7 @@ def process_git_request(fname, target_branch, source_branch, prj_dir)
 #  puts "Working Dir : " + working_dir
   Dir.chdir working_dir
 #  puts "pwd : " + Dir.pwd
-  git_cmd = "git log --oneline --no-abbrev-commit origin/" + target_branch + ".." + "origin/" + source_branch
+  git_cmd = "git log --oneline --no-abbrev-commit base_repo/" + target_branch + ".." + "origin/" + source_branch
 #  puts git_cmd
   out, err, status = Open3.capture3(git_cmd)
   if status.exitstatus != 0

.github/workflows/process-pull-request.yml

@@ -9,7 +9,7 @@ on:
   pull_request:
     branches:
       - '**'
-      - '!mainline'    
+      - '!mainline'
 
 permissions:
   contents: read
@@ -24,7 +24,18 @@ jobs:
         ruby-version: ['3.0']
 
     steps:
-    - uses: actions/checkout@v4
+    - name: Checkout PR branch
+      uses: actions/checkout@v4
+      with:
+        repository: ${{ github.event.pull_request.head.repo.full_name }}
+        fetch-depth: 0
+        ref: ${{ github.head_ref }}
+
+    - name: Checkout base branch
+      run: |
+        git remote add base_repo https://github.com/${{ github.repository }}.git
+        git fetch base_repo ${{ github.base_ref }}:${{ github.base_ref }}
+
     - name: Set up Ruby
     # To automatically get bug fixes and new Ruby versions for ruby/setup-ruby,
     # change this to (see https://github.com/ruby/setup-ruby#versioning):
@@ -39,8 +50,6 @@ jobs:
       run: |
         /usr/bin/pip3 install gitPython
         python -c "import sys; import git; print(sys.version)"
-        git fetch origin ${{ github.base_ref }}
-        git fetch origin ${{ github.head_ref }}
         git remote add linux https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
         git fetch --shallow-since="3 years ago" linux
         echo "Will run process-git-request.rb with:"