chore(ci): upgrade GitHub Actions to latest versions

- actions/checkout@v2 → @v4
- subosito/flutter-action@v1 → @v2

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: vincenzopalazzo

.github/workflows/build.yml

@@ -14,7 +14,7 @@ jobs:
           - stable
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - uses: subosito/flutter-action@v2
         with:
           channel: ${{matrix.channel}}

.github/workflows/codcoverage.yml

@@ -11,8 +11,8 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v2
-      - uses: subosito/flutter-action@v1
+      - uses: actions/checkout@v4
+      - uses: subosito/flutter-action@v2
         with:
           channel: 'stable'
       - name: Run tests with coverage

.github/workflows/release_dart.yml

@@ -19,7 +19,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: 'Checkout'
-        uses: actions/checkout@v2 # required!
+        uses: actions/checkout@v4 # required!
 
       - name: 'publish graphql to to Pub.dev'
         uses: k-paxian/dart-package-publisher@master

.github/workflows/release_flutter.yml

@@ -19,7 +19,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: 'Checkout'
-        uses: actions/checkout@v2 # required!
+        uses: actions/checkout@v4 # required!
 
       - name: 'publish graphql-flutter to to Pub.dev'
         uses: k-paxian/dart-package-publisher@master

.github/workflows/release_packages.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: 'Checkout'
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
       - name: 'graphql publish to to Pub.dev'
         uses: k-paxian/dart-package-publisher@master
         with:
@@ -26,7 +26,7 @@ jobs:
       - publishing_client
     steps:
       - name: 'Checkout'
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
         # FIXME: when we bump a new release, we can have problem
         # in dry mode because the new release is not on the pub.dev
         # yet

.github/workflows/test.yml

@@ -10,8 +10,8 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
-      - uses: subosito/flutter-action@v1
+      - uses: actions/checkout@v4
+      - uses: subosito/flutter-action@v2
         with:
           channel: 'stable'
       - name: Install dependencies