bitbucket-readable-commit-messages: support commits not on a branch

Commits not on a branch have an additional <div> added to them with the
message "This commit is not reachable from any branch or tag in this
repository. It may be from a fork outside of this repository." The extra
<div> breaks the selector which uses nth-child pseudo-class in userstyle
bitbucket-readable-commit-messages.user.css.

I noticed that the <div> with commit message doesn't have a `class`
attribute at all.  Rewrite the selector not to rely on the order of
elements.

Examples for tests:

  - Commit on a branch:
    https://bitbucket.org/andreyrybak/atlassian-tweaks/commits/d1ff7b1d2f4f9d6fed7c706f330eaa11c73d264f

  - Commit not on a branch:
    https://bitbucket.org/andreyrybak/atlassian-tweaks/commits/19ca4f537e454e15f4e3bf1f88ebc43c0e9c559a

bitbucket-readable-commit-messages.user.css

@@ -1,7 +1,7 @@
 /* ==UserStyle==
 @name        Bitbucket: readable commit messages
 @namespace   https://github.com/rybak/atlassian-tweaks
-@version     4
+@version     5
 @description Make commit messages on Bitbucket Cloud more readable
 @license     MIT
 @homepageURL https://github.com/rybak/atlassian-tweaks
@@ -16,7 +16,7 @@
 ==/UserStyle== */
 
 /*
- * Copyright (c) 2023 Andrei Rybak
+ * Copyright (c) 2023-2024 Andrei Rybak
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -43,20 +43,20 @@
  */
 
 /* border around the whole commit message */
-.css-1120ym1 > div:nth-child(1) > div:nth-child(3):not([data-qa="commit-list-container"]) {
+.css-1120ym1 > div:nth-child(1) > div:not([data-qa="commit-list-container"]):not([class]) {
 	border: borderWidth solid borderColor;
 	border-radius: borderRadius;
 	padding: paddingSize;
 }
 if monospaceEnable {
 	/* monospace text */
-	.css-1120ym1 > div:nth-child(1) > div:nth-child(3):not([data-qa="commit-list-container"]) {
+	.css-1120ym1 > div:nth-child(1) > div:not([data-qa="commit-list-container"]):not([class]) {
 		font-family: monospace;
 	}
 }
 
 /* make the subject line of commit message bold */
-.css-1120ym1 > div:nth-child(1) > div:nth-child(3):not([data-qa="commit-list-container"]) > p:first-child {
+.css-1120ym1 > div:nth-child(1) > div:not([data-qa="commit-list-container"]):not([class]) > p:first-child {
 	font-weight: bold;
 }
 }