Exclude maven-release leftovers from spotless

Spotless's generic format walks the filesystem and does not honor
.gitignore, so stray maven-release-plugin files (release.properties,
*.releaseBackup, pom.xml.next, pom.xml.tag) tripped spotless:check
locally even though they are gitignored. Exclude them explicitly.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015krtPy49YGqBERvq4yDjCa

Author: khatchad

pom.xml

@@ -163,6 +163,10 @@
                   <exclude>**/v1_astmanager/</exclude>
                   <exclude>mvnw.cmd</exclude>
                   <exclude>**/*.target</exclude>
+                  <exclude>**/release.properties</exclude>
+                  <exclude>**/*.releaseBackup</exclude>
+                  <exclude>**/pom.xml.next</exclude>
+                  <exclude>**/pom.xml.tag</exclude>
                 </excludes>
                 <trimTrailingWhitespace/>
                 <endWithNewline/>