Fix default merge style (go-gitea#20564)

Author: wxiaoguang

templates/repo/issue/view_content/pull.tmpl

@@ -357,6 +357,7 @@
 									'emptyCommit': {{.Issue.PullRequest.IsEmpty}},
 									'pullHeadCommitID': {{.PullHeadCommitID}},
 									'isPullBranchDeletable': {{.IsPullBranchDeletable}},
+									'defaultMergeStyle': {{.MergeStyle}},
 									'defaultDeleteBranchAfterMerge': {{$prUnit.PullRequestsConfig.DefaultDeleteBranchAfterMerge}},
 									'mergeMessageFieldPlaceHolder': {{$.locale.Tr "repo.editor.commit_message_desc"}},
 

web_src/js/components/PullRequestMergeForm.vue

@@ -145,7 +145,10 @@ export default {
 
   created() {
     this.mergeStyleAllowedCount = this.mergeForm.mergeStyles.reduce((v, msd) => v + (msd.allowed ? 1 : 0), 0);
-    this.switchMergeStyle(this.mergeForm.mergeStyles.find((e) => e.allowed)?.name, !this.mergeForm.canMergeNow);
+
+    let mergeStyle = this.mergeForm.mergeStyles.find((e) => e.allowed && e.name === this.mergeForm.defaultMergeStyle)?.name;
+    if (!mergeStyle) mergeStyle = this.mergeForm.mergeStyles.find((e) => e.allowed)?.name;
+    this.switchMergeStyle(mergeStyle, !this.mergeForm.canMergeNow);
   },
 
   mounted() {