Adds MR reference in job sidebar

In the refactor the `!` reference was missed
This commit adds it back and adds coverage for it.

app/assets/javascripts/jobs/components/commit_block.vue

@@ -46,7 +46,7 @@
         v-if="mergeRequest"
         :href="mergeRequest.path"
         class="js-link-commit link-commit"
-      >{{ mergeRequest.iid }}</a>
+      >!{{ mergeRequest.iid }}</a>
     </p>
 
     <p class="build-light-text append-bottom-0">

spec/javascripts/jobs/components/commit_block_spec.js

@@ -56,7 +56,7 @@ describe('Commit block', () => {
         props.mergeRequest.path,
       );
       expect(vm.$el.querySelector('.js-link-commit').textContent.trim()).toEqual(
-        props.mergeRequest.iid,
+        `!${props.mergeRequest.iid}`,
       );
     });
   });