ensure MergeRequestStore sha value never changes after instantiation

app/assets/javascripts/vue_merge_request_widget/stores/mr_widget_store.js

@@ -4,7 +4,7 @@ import { getStateKey } from '../dependencies';
 export default class MergeRequestStore {
 
   constructor(data) {
-    this.startingSha = data.diff_head_sha;
+    this.sha = data.diff_head_sha;
     this.setData(data);
   }
 
@@ -16,7 +16,6 @@ export default class MergeRequestStore {
     this.targetBranch = data.target_branch;
     this.sourceBranch = data.source_branch;
     this.mergeStatus = data.merge_status;
-    this.sha = data.diff_head_sha;
     this.commitMessage = data.merge_commit_message;
     this.commitMessageWithDescription = data.merge_commit_message_with_description;
     this.commitsCount = data.commits_count;
@@ -69,7 +68,7 @@ export default class MergeRequestStore {
     this.canMerge = !!data.merge_path;
     this.canCreateIssue = currentUser.can_create_issue || false;
     this.canCancelAutomaticMerge = !!data.cancel_merge_when_pipeline_succeeds_path;
-    this.hasSHAChanged = this.sha !== this.startingSha;
+    this.hasSHAChanged = this.sha !== data.diff_head_sha;
     this.canBeMerged = data.can_be_merged || false;
 
     // Cherry-pick and Revert actions related