Upgrade to Spring Boot 2.6.0-RC1.

Author: jxblum

gradle.properties

@@ -5,7 +5,7 @@ findbugsVersion=3.0.2
 # The Spring Boot & Spring Session version are the only required version properties.
 # The other Spring version properties are for overriding/testing purposes.
 springVersion=5.3.12
-springBootVersion=2.6.0-M3
+springBootVersion=2.6.0-RC1
 springDataBomVersion=2021.1.0-RC1
 springDataCommonsVersion=2.6.0-RC1
 springDataGeodeVersion=2.6.0-RC1