ci: move coverage to own workflow

.github/workflows/coverage.yml

@@ -0,0 +1,37 @@
+name: Coverage
+
+on:
+  push:
+    branches: [master]
+
+permissions:
+  contents: read
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  coverage:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install Rust
+        uses: actions-rust-lang/setup-rust-toolchain@v1.5.0
+        with:
+          components: llvm-tools-preview
+
+      - name: Install cargo-llvm-cov
+        uses: taiki-e/install-action@v2.18.9
+        with:
+          tool: cargo-llvm-cov
+
+      - name: Generate code coverage
+        run: cargo llvm-cov --workspace --all-features --codecov --output-path codecov.json
+
+      - name: Upload coverage to Codecov
+        uses: codecov/codecov-action@v3.1.4
+        with:
+          files: codecov.json
+          fail_ci_if_error: true