Build/Test Tools: Increase Gutenberg artifact retention.

It’s common for nuanced workflow run failures to be investigated over the course of several days following the initial run. In these cases, the entire workflow must be rerun even one only one or two jobs had failed because the artifact has expired.

This increases the artifact retention of the built Gutenberg asset from `1` day to `7` to help with this workflow.

See #65845.

git-svn-id: https://develop.svn.wordpress.org/trunk@63558 602fd350-edb4-49c9-b593-d223f7449a82

Author: desrosj

.github/workflows/reusable-prepare-gutenberg.yml

@@ -106,4 +106,4 @@ jobs:
           path: gutenberg/
           if-no-files-found: error
           include-hidden-files: true
-          retention-days: 1
+          retention-days: 7