Remove dead xml-apis dependency exclusions

[codeconsole]

xml-apis:xml-apis has not been reachable from any of these dependencies for several major versions, so the four exclusions are no-ops:

• hibernate-core 7.4.1.Final and hibernate-core-jakarta 5.6.15.Final never declare xml-apis. Hibernate's own POM already excludes it from every one of its dependencies, and mapping XML has been bound with JAXB (jakarta.xml.bind-api + jaxb-runtime) since Hibernate 6 dropped dom4j.
• commons-validator 1.9.0 no longer pulls commons-digester/xml-apis.

Verification

With the exclusions removed, dependencyInsight --dependency xml-apis finds no match on compileClasspath, runtimeClasspath, or testRuntimeClasspath for any of the three modules, and the full resolved dependency graphs are byte-identical to before.

The only publication change is the removal of three dead <exclusion> entries from the generated POMs (the fourth is on a compileOnly dependency, which is not published).

:grails-datamapping-validation:test, :grails-data-hibernate7-core:test and :grails-data-hibernate5-core:test pass (3066 tests, 0 failures), and aggregateStyleViolations reports no Checkstyle or CodeNarc violations.

[testlens-app]

✅ All tests passed ✅

⚠️ TestLens detected flakiness ⚠️

Test Summary

CI / Functional Tests (Java 25, indy=false, shard 1) > :grails-test-examples-gsp-sitemesh3:integrationTest

Test	Runs	Flakiness
EndToEndSpec > async multiple levels of layouts	❌ ✅	1% 🟡

🏷️ Commit: e469c27
▶️ Tests: 20003 executed
⚪️ Checks: 83/83 completed

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 54.7139%. Comparing base (4309d5b) to head (e469c27).

Additional details and impacted files

@@                Coverage Diff                 @@
##                8.0.x     #16279        +/-   ##
==================================================
- Coverage     54.7149%   54.7139%   -0.0010%     
  Complexity      20421      20421                
==================================================
  Files            2101       2101                
  Lines          100978     100978                
  Branches        17907      17907                
==================================================
- Hits            55250      55249         -1     
  Misses          37860      37860                
- Partials         7868       7869         +1     

see 5 files with indirect coverage changes

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