Check failed clang-format version

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: hjmjohnson

action.yml

@@ -23,6 +23,16 @@ runs:
             "https://raw.githubusercontent.com/InsightSoftwareConsortium/ITK/${ITK_BRANCH}/.pre-commit-config.yaml" \
             -o ITK.pre-commit-config.yaml
           CLANG_FORMAT_VERSION=$(grep -A 1 "mirrors-clang-format" ITK.pre-commit-config.yaml | tail -n 1 | cut -d: -f2 | tr -d ' v')
+          if [ -z "${CLANG_FORMAT_VERSION}" ]; then
+            echo "::error::Unable to determine clang-format version from ITK .pre-commit-config.yaml for branch '${ITK_BRANCH}'. The expected mirrors-clang-format revision entry was not found or could not be parsed."
+            rm -f ITK.pre-commit-config.yaml
+            exit 1
+          fi
+          if ! [[ "${CLANG_FORMAT_VERSION}" =~ ^[0-9]+(\.[0-9]+)*$ ]]; then
+            echo "::error::Invalid clang-format version parsed from ITK .pre-commit-config.yaml for branch '${ITK_BRANCH}': '${CLANG_FORMAT_VERSION}'. Expected a numeric version such as '18.1.8'."
+            rm -f ITK.pre-commit-config.yaml
+            exit 1
+          fi
           echo "clang_format_version=${CLANG_FORMAT_VERSION}" >> $GITHUB_OUTPUT
           echo "use_pixi=true" >> $GITHUB_OUTPUT
           echo "Detected clang-format version: ${CLANG_FORMAT_VERSION}"