fix: add proper id for branch in repository (#526)

Author: thielpa

server/application-server/src/main/java/de/tum/cit/aet/helios/branch/BranchRepository.java

@@ -6,7 +6,7 @@
 import org.springframework.stereotype.Repository;
 
 @Repository
-public interface BranchRepository extends JpaRepository<Branch, Long> {
+public interface BranchRepository extends JpaRepository<Branch, BranchId> {
   Optional<Branch> findByName(String name);
 
   Optional<Branch> findByNameAndRepositoryRepositoryId(String name, Long repositoryId);