Bump net.sf.saxon:Saxon-HE from 12.7 to 12.8 in /xml (#271)

Bumps net.sf.saxon:Saxon-HE from 12.7 to 12.8.

---
updated-dependencies:
- dependency-name: net.sf.saxon:Saxon-HE
  dependency-version: '12.8'
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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Author: dependabot[bot]

xml/pom.xml

@@ -12,7 +12,7 @@
     <dependencyCheck.version>12.1.3</dependencyCheck.version>
     <dependencyCheck.skip>false</dependencyCheck.skip>
     <dependencyCheck.threshold>7</dependencyCheck.threshold>
-    <saxon.version>12.7</saxon.version>
+    <saxon.version>12.8</saxon.version>
   </properties>
   <build>
     <plugins>