Add support for linking to Dart Sass pull requests

Author: nex3

.github/workflows/ci.yml

@@ -31,6 +31,9 @@ jobs:
       - uses: actions/checkout@v2
       - uses: dart-lang/setup-dart@v1
         with: {sdk: "${{ matrix.dart_channel }}"}
+      - uses: sass/clone-linked-repo@v1
+        with: {repo: sass/dart-sass, path: dart-sass}
+      - run: dart pub add "override:sass:{path: dart-sass}"
       - run: dart pub get
       - run: dart pub run grinder pkg-standalone-dev
       - name: Run tests
@@ -69,6 +72,9 @@ jobs:
       - uses: actions/checkout@v2
       - uses: dart-lang/setup-dart@v1
         with: {sdk: "${{ matrix.dart_channel }}"}
+      - uses: sass/clone-linked-repo@v1
+        with: {repo: sass/dart-sass, path: dart-sass}
+      - run: dart pub add "override:sass:{path: dart-sass}"
       - run: dart pub get
       - uses: actions/setup-node@v2
         with: {node-version: "${{ matrix.node_version }}"}
@@ -84,6 +90,9 @@ jobs:
     steps:
       - uses: actions/checkout@v2
       - uses: dart-lang/setup-dart@v1
+      - uses: sass/clone-linked-repo@v1
+        with: {repo: sass/dart-sass, path: dart-sass}
+      - run: dart pub add "override:sass:{path: dart-sass}"
       - run: dart pub get
       - name: Analyze dart
         run: dart analyze --fatal-warnings --fatal-infos lib tool test