GitGraph: Added e2e tests for deferred branch use.

In these tests, a new branch is created but then a commit is made
on the main branch before the new branch gets a commit. This
important to see what happens with rerouting of arrows.

Suggested by @nirname in PR review of mermaid-js#4927.

cypress/integration/rendering/gitGraph.spec.js

@@ -735,4 +735,34 @@ gitGraph TB:
       {}
     );
   });
+  it('36: should render GitGraph with branch that is not used immediately', () => {
+    imgSnapshotTest(
+      `gitGraph LR:
+      commit
+      branch x
+      checkout main
+      commit
+      checkout x
+      commit
+      checkout main
+      merge x
+      `,
+      {}
+    );
+  });
+  it('37: should render GitGraph with branch that is not used immediately | Vertical Branch', () => {
+    imgSnapshotTest(
+      `gitGraph TB:
+      commit
+      branch x
+      checkout main
+      commit
+      checkout x
+      commit
+      checkout main
+      merge x
+      `,
+      {}
+    );
+  });
 });