Merge pull request #262 from grails/renovate/spring-core

Update spring core to v5.3.9

Author: puneetbehl

gradle.properties

@@ -21,7 +21,7 @@ seleniumSafariDriverVersion=3.14.0
 seleniumVersion=3.14.0
 spockVersion=2.0-M3-groovy-3.0
 springBootVersion=2.5.2
-springVersion=5.3.8
+springVersion=5.3.9
 webdriverBinariesVersion=1.4
 
 # only required by sample apps