ci: Adopt conclusion job that summarizes ci status

Originally contributed by @messense in pyo3, copied their solution with
thanks.

.github/workflows/pr-check.yml → .github/workflows/ci.yaml

@@ -2,7 +2,7 @@ on:
   pull_request:
   merge_group:
 
-name: CI Check
+name: Continuous integration
 
 env:
   CARGO_TERM_COLOR: always
@@ -28,6 +28,7 @@ jobs:
   tests:
     if: ${{ github.event_name == 'merge_group' }}
     runs-on: ubuntu-latest
+    name: tests/${{ matrix.platform.rust-target }}/${{ matrix.rust }}
     strategy:
       matrix:
         rust:
@@ -49,6 +50,7 @@ jobs:
   cross_test:
     if: ${{ github.event_name == 'merge_group' }}
     runs-on: ubuntu-latest
+    name: cross_test/${{ matrix.platform.rust-target }}/${{ matrix.rust }}
     strategy:
       matrix:
         include:
@@ -67,3 +69,19 @@ jobs:
       - name: Install cross
         run: cargo install cross
       - run: ./scripts/cross-tests.sh "docs" ${{ matrix.rust }} ${{ matrix.target }}
+
+  conclusion:
+    needs:
+      - clippy
+      - tests
+      - cross_test
+    if: always()
+    runs-on: ubuntu-latest
+    steps:
+      - name: Result
+        run: |
+          jq -C <<< "${needs}"
+          # Check if all needs were successful or skipped.
+          "$(jq -r 'all(.result as $result | (["success", "skipped"] | contains([$result])))' <<< "${needs}")"
+        env:
+          needs: ${{ toJson(needs) }}