chore: Filter out non-semver versions in update_generation_config.sh (googleapis#11831)

Filter out non-semver versions in update_generation_config.sh. This is a
temporary fix for this release because it is causing the [generation
PR](googleapis#11822) on the
main branch to get the RC version of gapic-generator-java and fail the
compilation.

The file is
[templated](https://github.com/googleapis/sdk-platform-java/blob/main/hermetic_build/library_generation/owlbot/templates/java_library/.github/scripts/update_generation_config.sh)
in sdk-platform-java. There will be another fix for the template in
sdk-platform-java.

Author: blakeli0

.github/scripts/update_generation_config.sh

@@ -18,7 +18,17 @@ function get_latest_released_version() {
     group_id_url_path="$(sed 's|\.|/|g' <<< "${group_id}")"
     url="https://repo1.maven.org/maven2/${group_id_url_path}/${artifact_id}/maven-metadata.xml"
     xml_content=$(curl -s --fail "${url}")
-    latest=$(xmllint --xpath 'metadata/versioning/latest/text()' - <<< "${xml_content}")
+
+    # 1. Extract all version tags
+    # 2. Strip the XML tags to leave just the version numbers
+    # 3. Filter for strictly numbers.numbers.numbers (e.g., 2.54.0)
+    # 4. Sort by version (V) and take the last one (tail -n 1)
+    latest=$(echo "${xml_content}" \
+      | grep -oE '<version>[0-9]+\.[0-9]+\.[0-9]+</version>' \
+      | sed -E 's/<[^>]+>//g' \
+      | sort -V \
+      | tail -n 1)
+
     if [[ -z "${latest}" ]]; then
         echo "The latest version of ${group_id}:${artifact_id} is empty."
         echo "The returned json from maven.org is invalid: ${json_content}"
@@ -174,4 +184,4 @@ if [ -z "${pr_num}" ]; then
 else
   git push
   gh pr edit "${pr_num}" --title "${title}" --body "${title}"
-fi
+fi