SOLR-15710: Fix solr-upgrade-notes.adoc URL in CHANGES.txt

[uzzz]

https://issues.apache.org/jira/browse/SOLR-15710

Description

URL was pointing to the old https://github.com/apache/lucene-solr wiped repo in CHANGES.txt.

Solution

Replace it with the correct one.

Checklist

Please review the following and check all that apply:

• I have reviewed the guidelines for How to Contribute and my code conforms to the standards described there to the best of my ability.
• I have created a Jira issue and added the issue ID to my pull request title.
• I have given Solr maintainers access to contribute to my PR branch. (optional but recommended)
• I have developed this patch against the main branch.
• I have run ./gradlew check.
• I have added tests for my changes.
• I have added documentation for the Reference Guide