PR sha is the wrong one, fix it

Signed-off-by: Nicolas Belouin <nicolas.belouin@suse.com>

.gitea/workflows/pr_project.yaml

@@ -40,7 +40,9 @@ jobs:
           PROJECT="$(grep PROJECT .obs/common.py | sed 's/PROJECT = "\(.*\)"/\1/')"
           python3 .obs/render_meta.py --pr ${{ gitea.event.number }} --scm-url "${SCM_URL}" | osc meta prj "${PROJECT}:Staging:PR-${{ gitea.event.number }}" -F -
           fi
-      - run: |
+      - env:
+          GIT_SHA: ${{ gitea.event.pull_request.head.sha }}
+        run: |
           if [ "${{ gitea.event.action }}" != "closed" ]; then
           PROJECT="$(grep PROJECT .obs/common.py | sed 's/PROJECT = "\(.*\)"/\1/')"
           export OBS_PROJECT="${PROJECT}:Staging:PR-${{ gitea.event.number }}"