ci(vite-plugin-angular): run decorator/signal drift detectors in conformance CI

The decorator and signal-API coverage detectors skip when ANGULAR_SOURCE_DIR is
unset, so they never ran in CI. Sparse-checkout the upstream sources they read
(packages/core/src and the ngtsc initializer-function list) alongside the
compliance fixtures, and run both specs in the conformance job so the drift
guards execute against every Angular version in the matrix.

Addresses a CodeRabbit review finding on #2383.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: brandonroberts

.github/workflows/conformance.yml

@@ -43,7 +43,11 @@ jobs:
         run: pnpm install --frozen-lockfile --prefer-offline
       - name: Download Angular ${{ matrix.angular-major }} compliance fixtures
         run: bash packages/vite-plugin-angular/scripts/setup-conformance.sh ${{ matrix.angular-major }}
-      - name: Run conformance tests
+      - name: Run conformance and upstream-drift tests
         env:
           ANGULAR_SOURCE_DIR: .angular-conformance
-        run: pnpm exec vitest run packages/vite-plugin-angular/src/lib/compiler/conformance.spec.ts
+        run: >-
+          pnpm exec vitest run
+          packages/vite-plugin-angular/src/lib/compiler/conformance.spec.ts
+          packages/vite-plugin-angular/src/lib/compiler/decorator-coverage.spec.ts
+          packages/vite-plugin-angular/src/lib/compiler/signal-api-coverage.spec.ts

packages/vite-plugin-angular/scripts/setup-conformance.sh

@@ -71,7 +71,12 @@ if ! git clone --depth 1 --branch "$VERSION" --filter=blob:none --sparse \
 fi
 
 cd "$TARGET"
-git sparse-checkout set packages/compiler-cli/test/compliance/test_cases
+# test_cases drives conformance.spec; core/src and the ngtsc initializer-function
+# list are the upstream sources the decorator / signal-API drift detectors read.
+git sparse-checkout set \
+  packages/compiler-cli/test/compliance/test_cases \
+  packages/core/src \
+  packages/compiler-cli/src/ngtsc/annotations/directive/src
 
 echo "Done. $(find packages/compiler-cli/test/compliance/test_cases -name '*.ts' | wc -l | tr -d ' ') test files downloaded."
 echo "Run: ANGULAR_SOURCE_DIR=$TARGET npx vitest run packages/vite-plugin-angular/src/lib/compiler/conformance.spec.ts"