Update post-install message to be more consistent with UI text guidelines

The Needs Review Queue Bot → tested this issue. It either no longer applies to Drupal core, or fails the Drupal core commit checks. Therefore, this issue status is now "Needs work".

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Attached patch against Drupal 10.1.x

Patch #64 is not applied for Drupal 10.1.x so Inter-diff file is not added.