Update pipeline (didn't allow PR branches other than 'main')

Author: nohli

.github/workflows/flutter_build_example.yml

@@ -15,8 +15,6 @@ jobs:
     steps:
       - name: Checkout repository
         uses: actions/checkout@v4
-        with:
-          ref: ${{ github.head_ref }}
       - name: Setup Java
         uses: actions/setup-java@v4
         with:

.github/workflows/flutter_checks.yml

@@ -15,8 +15,6 @@ jobs:
     steps:
       - name: Checkout repository
         uses: actions/checkout@v4
-        with:
-          ref: ${{ github.head_ref }}
       - name: Install Flutter
         uses: subosito/flutter-action@v2
       - name: Disable analytics
@@ -31,8 +29,6 @@ jobs:
     steps:
       - name: Checkout repository
         uses: actions/checkout@v4
-        with:
-          ref: ${{ github.head_ref }}
       - name: Install Flutter
         uses: subosito/flutter-action@v2
       - name: Disable analytics
@@ -49,8 +45,6 @@ jobs:
     steps:
       - name: Checkout repository
         uses: actions/checkout@v4
-        with:
-          ref: ${{ github.head_ref }}
       - name: Install Flutter
         uses: subosito/flutter-action@v2
       - name: Disable analytics
@@ -67,8 +61,6 @@ jobs:
     steps:
       - name: Checkout repository
         uses: actions/checkout@v4
-        with:
-          ref: ${{ github.head_ref }}
       - name: Install Flutter
         uses: subosito/flutter-action@v2
       - name: Disable analytics
@@ -85,8 +77,6 @@ jobs:
     steps:
       - name: Checkout repository
         uses: actions/checkout@v4
-        with:
-          ref: ${{ github.head_ref }}
       - name: Install Flutter
         uses: subosito/flutter-action@v2
       - name: Disable analytics

.github/workflows/pub_publish.yml

@@ -10,8 +10,6 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-        with:
-          ref: ${{ github.head_ref }}
       - name: Publish
         uses: k-paxian/dart-package-publisher@v1.6
         with:

.github/workflows/pub_publish_dry_run.yml

@@ -12,8 +12,6 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-        with:
-          ref: ${{ github.head_ref }}
       - name: Publish dry run
         uses: k-paxian/dart-package-publisher@v1.6
         with:

.github/workflows/pub_score.yml

@@ -13,8 +13,6 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-        with:
-          ref: ${{ github.head_ref }}
       - uses: axel-op/dart-package-analyzer@v3
         id: workflow
         with: