Minor UI fixes (#14926)

* disable fork button when not signed in

* fix commit body styling on PR page

* fixup! fix commit body styling on PR page

web_src/less/_repository.less

@@ -2768,12 +2768,17 @@ tbody.commit-list {
 
 .commit-body {
   white-space: pre-wrap;
+  line-height: initial;
 }
 
 .repository:not(.diff) {
-  .commit-body {
+  .commit-body { // commit history list
     margin: 0;
   }
+
+  .timeline-item .commit-body { // PR-comment
+    margin-left: 40px;
+  }
 }
 
 .git-notes.top {