build: fix java 11 build

Author: hauner

gradle/libs.versions.toml

@@ -1,7 +1,8 @@
 [versions]
 openapiparser = "2026.3-SNAPSHOT"
 
-checker = "4.2.2"
+#checker = "4.2.2" requires jdk 17
+checker = "3.55.1
 
 [libraries]
 checker = { module = "org.checkerframework:checker", version.ref = "checker" }