cd: lock flutter version to 3.3

.github/workflows/spotube-nightly.yml

@@ -13,6 +13,7 @@ jobs:
       - uses: subosito/[email protected]
         with:
           cache: true
+          flutter-version: '3.3.8'
       - name: Get current date
         id: date
         run: echo "::set-output name=date::$(date +'%Y-%m-%d')"
@@ -56,6 +57,7 @@ jobs:
       - uses: subosito/[email protected]
         with:
           cache: true
+          flutter-version: '3.3.8'
       - run: |
           sudo apt-get update -y
           sudo apt-get install -y clang cmake ninja-build pkg-config libgtk-3-dev make python3-pip python3-setuptools patchelf desktop-file-utils libgdk-pixbuf2.0-dev fakeroot strace fuse
@@ -90,6 +92,7 @@ jobs:
       - uses: subosito/[email protected]
         with:
           cache: true
+          flutter-version: '3.3.8'
       - run: |
           choco install sed make yq -y
           yq -i '.version |= sub("\+\d+", "-nightly-")' pubspec.yaml
@@ -120,6 +123,7 @@ jobs:
       - uses: subosito/[email protected]
         with:
           cache: true
+          flutter-version: '3.3.8'
       - run: brew install yq
       - run: yq -i '.version |= sub("\+\d+", "-nightly-")' pubspec.yaml
       - run: yq -i '.version += strenv(GITHUB_RUN_NUMBER)' pubspec.yaml