Use master branch for github actions

.github/workflows/pull_request_full_build.yml

@@ -4,7 +4,6 @@ on:
   pull_request:
     branches:
       - master
-      - java21
 
 jobs:
   build-lang:
@@ -93,12 +92,6 @@ jobs:
           do git clone https://github.com/ballerina-platform/${module_name}.git; \
           done
 
-      - name: Checkout non-default branch
-        run: |
-          for module_name in $(jq -r '.standard_library| .[] | select(.level==${{ matrix.level }}) | .name' extensions.json); do \
-          cd $module_name && git fetch origin && git checkout -t origin/java21 && cd ..; \
-          done
-
       - name: Update Lang Version in Module
         run: |
           for module_name in $(jq -r '.standard_library| .[] | select(.level==${{ matrix.level }}) | .name' extensions.json); do \
@@ -139,10 +132,6 @@ jobs:
           distribution: 'temurin'
           java-version: '21.0.3'
 
-      - name: Checkout non-default branch
-        run: |
-          git fetch origin && git checkout -t origin/java21
-
       - name: Download Ballerina Lang Artifacts
         uses: actions/download-artifact@v4
         with:

.github/workflows/pull_request_ubuntu_build.yml

@@ -15,7 +15,6 @@ on:
       - native-build
       - revert-client-decl-master
       - query-grouping-aggregation
-      - java21
 
 jobs:
   ubuntu_build:

.github/workflows/pull_request_windows_build.yml

@@ -15,7 +15,6 @@ on:
       - native-build
       - revert-client-decl-master
       - query-grouping-aggregation
-      - java21
 jobs:
   windows_build:
     name: Build with some tests on Windows