Update Mermaid to v8.2.6

This fixes a regression where an underscore in labels no
longer worked:
https://github.com/knsv/mermaid/releases

app/assets/javascripts/branches/divergence_graph.js

@@ -25,6 +25,11 @@ export default endpoint => {
   const names = [...document.querySelectorAll('.js-branch-item')].map(
     ({ dataset }) => dataset.name,
   );
+
+  if (names.length === 0) {
+    return true;
+  }
+
   return axios
     .get(endpoint, {
       params: { names },

changelogs/unreleased/sh-suppress-diverging-count-commits-request.yml

+---
+title: Skip requesting diverging commit counts if no branches are listed
+merge_request: 32496
+author:
+type: performance

spec/frontend/branches/divergence_graph_spec.js

@@ -25,13 +25,25 @@ describe('Divergence graph', () => {
     mock.restore();
   });
 
-  it('calls axos get with list of branch names', () =>
+  it('calls axios get with list of branch names', () =>
     init('/-/diverging_counts').then(() => {
       expect(axios.get).toHaveBeenCalledWith('/-/diverging_counts', {
         params: { names: ['master', 'test/hello-world'] },
       });
     }));
 
+  describe('no branches listed', () => {
+    beforeEach(() => {
+      document.body.innerHTML = `<div></div>`;
+    });
+
+    it('avoids requesting diverging commit counts', () => {
+      expect(axios.get).not.toHaveBeenCalledWith('/-/diverging_counts');
+
+      init('/-/diverging_counts');
+    });
+  });
+
   it('creates Vue components', () =>
     init('/-/diverging_counts').then(() => {
       expect(document.querySelector('[data-name="master"]').innerHTML).not.toEqual('');