github/actions: In codeowners workflow fetch PR head ref for forked repos.

This commit adjusts the GitHub Action workflow to properly handle pull requests
from forked repositories. It removes the previous approach of calculating
fetch-depth and directly fetching the PR merge ref. Instead, it now checks out
the base ref with full history and then explicitly fetches and checks out the
PR's head ref. This change ensures that the workflow has access to the correct
set of changes, even when the PR is from a fork, and mitigates the potential
issue with the 'bad object' error seen when trying to access the head commit of
a forked repo.

Signed-off-by: Nikolay Martyanov <[email protected]>

Author: OhmSpectator

.github/workflows/request_codeowners_review.yml

@@ -11,18 +11,16 @@ jobs:
     permissions:
       pull-requests: write
     steps:
-      - name: Calculate fetch-depth
-        id: calc
-        run: echo "depth=$(echo $((${{ github.event.pull_request.commits }} + 1)))" >> $GITHUB_OUTPUT
-
-      - name: Fetch the pull request head
-        run: git fetch origin +refs/pull/${{ github.event.pull_request.number }}/merge
-
       - name: Checkout code
         uses: actions/checkout@v4
         with:
-          ref: ${{ github.event.pull_request.head.sha }}
-          fetch-depth: ${{ steps.calc.outputs.depth }}
+          ref: ${{ github.base_ref }}
+          fetch-depth: 0
+
+      - name: Fetch the PR's head ref
+        run: |
+          git fetch origin ${{ github.event.pull_request.head.sha }}:${{ github.event.pull_request.head.ref }}
+          git checkout ${{ github.event.pull_request.head.ref }}
 
       - name: Auto request review
         env:
@@ -32,7 +30,7 @@ jobs:
           # Get changed files in this pull request
           echo "Checking base: ${{ github.event.pull_request.base.sha }}"
           echo "Checking head: ${{ github.event.pull_request.head.sha }}"
-          for changed_file in $(git diff --name-only ${{ github.event.pull_request.base.sha }} ${{ github.event.pull_request.head.sha }}); do
+          for changed_file in $(git diff --name-only ${{ github.event.pull_request.base.sha }}...HEAD); do
             echo "Checking $changed_file"
             while read -r line; do
               # Get pattern of the files owned