adjust branch name and require Maven 3.9.9

Author: oliverlietz

.github/workflows/maven.yml

@@ -2,9 +2,9 @@ name: CI
 
 on:
   push:
-    branches: [ "master" ]
+    branches: [ "main" ]
   pull_request:
-    branches: [ "master" ]
+    branches: [ "main" ]
   workflow_dispatch:
 
 jobs:
@@ -21,5 +21,5 @@ jobs:
         with:
           distribution: 'temurin'
           java-version: ${{ matrix.java-version }}
-      - run: mvn wrapper:wrapper -Dmaven="3.9.5"
+      - run: mvn wrapper:wrapper -Dmaven="3.9.9"
       - run: ./mvnw verify --batch-mode --no-transfer-progress --file pom.xml