Start building against Spring Framework 6.1.8 snapshots

See gh-40828

Author: wilkinsona

gradle.properties

@@ -13,7 +13,7 @@ junitJupiterVersion=5.10.2
 kotlinVersion=1.9.24
 mavenVersion=3.9.4
 nativeBuildToolsVersion=0.9.28
-springFrameworkVersion=6.1.7
+springFrameworkVersion=6.1.8-SNAPSHOT
 tomcatVersion=10.1.24
 
 kotlin.stdlib.default.dependency=false