Make test work with different default branch config

On a system configured with a different default branch name, doGitInitTestRepository
will create a repository with a branch named differently, and so further tests
would break:

  --- FAIL: TestGit/HTTP/PushCreate/SuccessfullyPushAndCreateTestRepository (0.02s)
      git_helper_for_declarative_test.go:167:
          	Error Trace:	git_helper_for_declarative_test.go:167
          	Error:      	Received unexpected error:
          	            	exit status 1 - error: src refspec master does not match any
          	            	error: failed to push some refs to 'http://127.0.0.1:3003/user2/repo-tmp-push-create-http.git'
          	Test:       	TestGit/HTTP/PushCreate/SuccessfullyPushAndCreateTestRepository
  git_test.go:587:
      	Error Trace:	git_test.go:587
      	Error:      	Received unexpected error:
      	            	repository does not exist [id: 0, uid: 0, owner_name: user2, name: repo-tmp-push-create-http]
      	Test:       	TestGit/HTTP/PushCreate

Author: mscherer

integrations/git_helper_for_declarative_test.go

@@ -139,6 +139,10 @@ func doGitInitTestRepository(dstPath string) func(*testing.T) {
 	return func(t *testing.T) {
 		// Init repository in dstPath
 		assert.NoError(t, git.InitRepository(dstPath, false))
+		repo, err := git.OpenRepository(dstPath)
+		assert.NoError(t, err)
+		assert.NoError(t, repo.SetDefaultBranch("master"))
+		assert.NoError(t, repo.Close())
 		assert.NoError(t, os.WriteFile(filepath.Join(dstPath, "README.md"), []byte(fmt.Sprintf("# Testing Repository\n\nOriginally created in: %s", dstPath)), 0644))
 		assert.NoError(t, git.AddChanges(dstPath, true))
 		signature := git.Signature{