Fix GIT_COMMIT_HASH not set in Flatpak builds (#12725)

The env var check was gated inside the .git directory check, so
Flatpak builds (which exclude .git from the sandbox) always fell
back to "0000000". Lift the env var check to top level and inject
the commit hash into the Flatpak manifest via build-options.env.

.github/workflows/build_all.yml

@@ -170,7 +170,7 @@ jobs:
           git_commit_hash="${{ github.event.pull_request.head.sha }}"
         else
           ver=V$ver_pure
-          git_commit_hash=""
+          git_commit_hash="${{ github.sha }}"
         fi
         echo "ver=$ver" >> $GITHUB_ENV
         echo "ver_pure=$ver_pure" >> $GITHUB_ENV
@@ -197,6 +197,11 @@ jobs:
         sed -i '0,/^finish-args:/s//build-options:\n  no-debuginfo: true\n  strip: true\nfinish-args:/' \
           scripts/flatpak/io.github.orcaslicer.OrcaSlicer.yml
       shell: bash
+    - name: Inject git commit hash into Flatpak manifest
+      run: |
+        sed -i "/name: OrcaSlicer/{n;s|buildsystem: simple|buildsystem: simple\n    build-options:\n      env:\n        git_commit_hash: \"$git_commit_hash\"|}" \
+          scripts/flatpak/io.github.orcaslicer.OrcaSlicer.yml
+      shell: bash
     - uses: flatpak/flatpak-github-actions/flatpak-builder@master
       with:
         bundle: OrcaSlicer-Linux-flatpak_${{ env.ver }}_${{ matrix.variant.arch }}.flatpak