Bump checkstyle from 6.19 to 8.18

Bumps [checkstyle](https://github.com/checkstyle/checkstyle) from 6.19 to 8.18.
- [Release notes](https://github.com/checkstyle/checkstyle/releases)
- [Commits](checkstyle/checkstyle@checkstyle-6.19...checkstyle-8.18)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

pom.xml

@@ -70,7 +70,7 @@
 
         <maven-surefire-and-failsafe-plugin.version>2.21.0</maven-surefire-and-failsafe-plugin.version>
 
-        <checkstyle.version>6.19</checkstyle.version>
+        <checkstyle.version>8.18</checkstyle.version>
     </properties>
 
     <dependencies>