github: fix self-hosted runner checkout issues

The unified workflow had two critical issues with repository checkout
on self-hosted runners. For pull requests, it attempted to fetch
non-existent merge refs like "35/merge". For push events, it used
incomplete HTTPS URLs missing the .git suffix.

This fixes both by using proper GitHub PR refs (refs/pull/N/head)
and complete HTTPS clone URLs with .git suffix for the public repository.

Fixes: 1b74004 ("github: unify self-hosted runner workflows")
Generated-by: Claude AI
Signed-off-by: Daniel Gomez <[email protected]>

Author: dkruces

.github/workflows/kdevops.yml

@@ -179,29 +179,27 @@ jobs:
         run: |
           set -euxo pipefail
 
-          # More efficient approach similar to actions/checkout
-          if [[ -d ".git" ]]; then
-            # Repo exists - clean and update (like actions/checkout)
-            git clean -ffdx
-            git reset --hard HEAD
-            # Ensure correct remote URL
-            git remote set-url origin $GITHUB_SERVER_URL/$GITHUB_REPOSITORY
-            git fetch --depth=1 origin ${{ github.ref_name }}
-            git reset --hard FETCH_HEAD
+          # Start fresh
+          rm -rfv ./* ./.* 2>/dev/null || true
+
+          # Clone repository (with mirror optimization when available)
+          if [[ -f "/mirror/kdevops.git/HEAD" ]]; then
+            git clone --verbose --progress \
+              --reference /mirror/kdevops.git \
+              --depth=1 \
+              ${{ github.server_url }}/${{ github.repository }}.git .
           else
-            # No repo - fresh clone with local mirror optimization
-            if [[ -f "/mirror/kdevops.git/HEAD" ]]; then
-              git clone --verbose --progress \
-                --reference /mirror/kdevops.git \
-                --depth=1 \
-                --branch ${{ github.ref_name }} \
-                $GITHUB_SERVER_URL/$GITHUB_REPOSITORY .
-            else
-              git clone --verbose --progress \
-                --depth=1 \
-                --branch ${{ github.ref_name }} \
-                $GITHUB_SERVER_URL/$GITHUB_REPOSITORY .
-            fi
+            git clone --verbose --progress \
+              --depth=1 \
+              ${{ github.server_url }}/${{ github.repository }}.git .
+          fi
+
+          # Checkout the appropriate ref based on event type
+          if [[ "${{ github.event_name }}" == "pull_request" ]]; then
+            git fetch --depth=1 origin refs/pull/${{ github.event.number }}/head:pr-branch
+            git checkout pr-branch
+          else
+            git checkout ${{ github.sha }}
           fi
 
       - name: Configure kdevops