Update subosito/flutter-action action to v2 (#188)

Co-authored-by: Renovate Bot <[email protected]>

Author: renovate[bot]

.github/workflows/dart-ci.yaml

@@ -15,7 +15,7 @@ jobs:
         os: [ ubuntu-latest, windows-latest, macos-latest ]
     steps:
       - uses: actions/checkout@v2
-      - uses: subosito/flutter-action@v1
+      - uses: subosito/flutter-action@v2
         with:
           flutter-version: '2.8.1'
       - uses: dart-lang/setup-dart@v1

.github/workflows/release.yaml

@@ -23,7 +23,7 @@ jobs:
 
     steps:
       - uses: actions/checkout@v2
-      - uses: subosito/flutter-action@v1
+      - uses: subosito/flutter-action@v2
         with:
           flutter-version: '2.8.1'
       - uses: dart-lang/setup-dart@v1