Merge build and install jobs

Ideally, the two jobs should remain separated. The `install` job would
use almost the same `matrix` (minus `target`) as the `build` job and
have the same `needs` and `if` as the `test` job. This would however
make a duplicated and error-prone `matrix` for the two jobs, and sharing
a `matrix` between jobs is currently not possible with GitHub Actions
(neither directly, nor using YAML anchors, other options were too
 cumbersome when writing this). Consequently, for the sake of
maintainability, the two jobs are merged for now.

.github/workflows/build_test.yaml

@@ -61,7 +61,7 @@ jobs:
 
     strategy:
       matrix:
-        backend: &build_backends
+        backend:
           - name: openmp
             image: gcc
             compiler:
@@ -185,28 +185,14 @@ jobs:
           path: tests_${{ matrix.backend.name }}.tar
         if: ${{ matrix.target.name == 'native' }}
 
-  # consume the project in another project
-  install:
-    runs-on: ubuntu-latest
-
-    needs:
-      - check_docker_files
-      - build
-
-    # run this job even if build_base did not run
-    if: ${{ ! cancelled() && needs.build.result == 'success' }}
-
-    strategy:
-      matrix:
-        backend:
-          # use the same backends matrix as the `build` job
-          <<: *build_backends
-
-    steps:
-      - name: Checkout built branch
-        uses: actions/checkout@v4
-        with:
-          submodules: recursive
+      # consume the project in a dummy project
+      # ideally, this part should be executed in a different job using almost
+      # the same `matrix` (minus `target`) as the `build` job and having the
+      # same `needs` and `if` as the `test` job; this would however make a
+      # duplicated and error-prone `matrix`, and sharing a `matrix` between
+      # jobs is currently not possible with GitHub Actions (neither directly,
+      # nor using YAML anchors, other options were too cumbersome when writing
+      # this); consequently, this part is just here for now
 
       - name: Prepare as subdirectory
         run: |
@@ -225,6 +211,7 @@ jobs:
             -DCMAKE_CXX_STANDARD=17 \
             ${{ matrix.backend.cmake_flags.kokkos }} \
             ${{ matrix.backend.cmake_flags.kokkos_fft }} \
+            ${{ matrix.target.cmake_flags }} \
             install_test/as_subdirectory
           docker run -v ${{ github.workspace }}:/work ghcr.io/cexa-project/kokkos-fft/base_${{ matrix.backend.image }}_${{ needs.check_docker_files.outputs.image_suffix }}:${{ needs.check_docker_files.outputs.image_tag }} \
           cmake --build install_test/as_subdirectory/build
@@ -255,7 +242,8 @@ jobs:
             -DCMAKE_C_COMPILER=${{ matrix.backend.compiler.c }} \
             -DCMAKE_CXX_COMPILER=${{ matrix.backend.compiler.cxx }} \
             -DCMAKE_CXX_STANDARD=17 \
-            ${{ matrix.backend.cmake_flags.kokkos_fft }}
+            ${{ matrix.backend.cmake_flags.kokkos_fft }} \
+            ${{ matrix.target.cmake_flags }}
           docker run -v ${{ github.workspace }}:/work ghcr.io/cexa-project/kokkos-fft/base_${{ matrix.backend.image }}_${{ needs.check_docker_files.outputs.image_suffix }}:${{ needs.check_docker_files.outputs.image_tag }} \
             cmake --build build_kokkos_fft -j $(( $(nproc) * 2 + 1 ))
           docker run -v ${{ github.workspace }}:/work ghcr.io/cexa-project/kokkos-fft/base_${{ matrix.backend.image }}_${{ needs.check_docker_files.outputs.image_suffix }}:${{ needs.check_docker_files.outputs.image_tag }} \