changlogger: When amending, do not preserve default link (#39868)

When doing `changelogger write --amend`, we normally preserve the
prologue, epilogue, and link unless these are overridden on the command
line.

An edge case is when you're amending version 1.2.3-beta to turn it into
1.2.3 release, and the link is the default link like
`https://example.com/diff/1.2.2...1.2.3-beta`. In this situation we
don't want to keep that link, we want to replace it with the new default
`https://example.com/diff/1.2.2...1.2.3`.

Also, when building changelogger, we have to install before trying to run it.

Committed via a GitHub action: https://github.com/Automattic/jetpack/actions/runs/11487859862

Upstream-Ref: Automattic/jetpack@07e18c2

composer.json

@@ -15,7 +15,7 @@
 	},
 	"require-dev": {
 		"yoast/phpunit-polyfills": "^1.1.1",
-		"automattic/jetpack-changelogger": "^4.2.6",
+		"automattic/jetpack-changelogger": "^4.2.7-alpha",
 		"automattic/wordbless": "@dev"
 	},
 	"suggest": {