CI: the Linux portable job runs the [portable] tests too, as the Windows and macOS jobs do

So the CPU fast-feedback indexer's portable case (and the other cross-platform checks) runs on Linux,
macOS and Windows.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015CeEGgpKdfkCTJb3YNMJcu

.gitea/workflows/build_and_test.yml

@@ -79,6 +79,14 @@ jobs:
           mkdir -p build
           cd build
           cmake -G Ninja -DJFJOCH_VIEWER_ONLY=ON -DJFJOCH_USE_CUDA=${{ matrix.use_cuda }} ${{ env.LINUX_CMAKE_FLAGS }} -DCMAKE_BUILD_TYPE=Release ..
+      # The quick cross-platform checks (tests/PortableTest.cpp and the [portable] cases), as on the
+      # Windows and macOS jobs, before anything is packaged. CPU-only cases.
+      - name: Portable tests
+        shell: bash
+        run: |
+          cd build
+          ninja -j16 jfjoch_portable_test
+          cd tests && ./jfjoch_portable_test "[portable]"
       - name: Build viewer, rugnux and XDS plugin tgz
         shell: bash
         run: |