Use Correct PR Numbers In Code Freeze Changelog Command (#40096)

* Fixed Changelog PR Number Markdown

This makes the regex for replacing the number with a
markdown link more strict. Previously it was converting
[#PRNUM] to [[#PRNUM]] and would also add a markdown link
even if one was only present. This solves those two issues.

* Deepen Code Freeze Changelog Checkout

By default our remote branch checkout performs a shallow checkout. This
results in the Jetpack Changelogger appending the wrong PR number
when we generate the changelog for the `readme.txt` file. Here we are
deepening the checkout to resolve the problem.

tools/monorepo-utils/src/code-freeze/commands/changelog/lib/index.ts

@@ -54,8 +54,8 @@ const updateReleaseChangelogs = async (
 
 	// Convert PR number to markdown link.
 	nextLog = nextLog.replace(
-		/\[#(\d+)\]/g,
-		'[$&](https://github.com/woocommerce/woocommerce/pull/$1)'
+		/\[#(\d+)\](?!\()/g,
+		'[#$1](https://github.com/woocommerce/woocommerce/pull/$1)'
 	);
 
 	readme = readme.replace(
@@ -81,7 +81,8 @@ export const updateReleaseBranchChangelogs = async (
 ): Promise< { deletionCommitHash: string; prNumber: number } > => {
 	const { owner, name, version } = options;
 	try {
-		await checkoutRemoteBranch( tmpRepoPath, releaseBranch );
+		// Do a full checkout so that we can find the correct PR numbers for changelog entries.
+		await checkoutRemoteBranch( tmpRepoPath, releaseBranch, false );
 	} catch ( e ) {
 		if ( e.message.includes( "couldn't find remote ref" ) ) {
 			Logger.error(