chore(deps): update kotlin monorepo to v1.8.0 (#358)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

gradle.properties

@@ -8,7 +8,7 @@ micronautTestVersion=4.0.0-SNAPSHOT
 
 groovyVersion=4.0.6
 spockVersion=2.3-groovy-4.0
-kotlinVersion=1.7.20
+kotlinVersion=1.8.0
 
 title=Micronaut Servlet
 projectDesc=Provides integration between Micronaut and the Servlet API