5.1.1 release failed due to SNAPSHOT version in preview modules

[suztomo]

Describe the bug

The 5.1.1 release failed: http://sponge2/058943ca-e952-4e2a-b87f-f4fde6a990ff

Indeed, the source tree has "SNAPSHOT" versions:

suztomo@suztomo-macbookpro.roam.internal ~/spring-cloud-gcp
~/spring-cloud-gcp $ git log -1
commit 731db51ab7e76fd53fa940c367f6467ef18b9d56 (HEAD, tag: v5.1.1)
Author: release-please[bot] <55107282+release-please[bot]@users.noreply.github.com>
Date:   Fri Mar 29 14:39:33 2024 -0400

    chore(main): release 5.1.1 (#2725)
    
    * chore(main): release 5.1.1
    
    * chore(main): release 5.1.1
    
    ---------
    
    Co-authored-by: release-please[bot] <55107282+release-please[bot]@users.noreply.github.com>
suztomo@suztomo-macbookpro.roam.internal ~/spring-cloud-gcp
~/spring-cloud-gcp $ find . -name pom.xml |xargs grep SNAPSHOT
./spring-cloud-generator/showcase/showcase-spring-starter/pom.xml:      <version>0.0.1-SNAPSHOT</version>
./spring-cloud-previews/google-iam-policy-spring-starter/pom.xml:    <version>5.1.1-SNAPSHOT</version><!-- {x-version-update:spring-cloud-gcp:current} -->
./spring-cloud-previews/google-cloud-translate-spring-starter/pom.xml:    <version>5.1.1-SNAPSHOT</version><!-- {x-version-update:spring-cloud-gcp:current} -->

Why didn't Release Please bump the version in the release pull request #2725 ?

~/spring-cloud-gcp $ grep spring-cloud-gcp versions.txt 
spring-cloud-gcp:5.1.1:5.1.1