Start building against Spring Data 2021.2.1 snapshots

See gh-31374

spring-boot-project/spring-boot-dependencies/build.gradle

@@ -1677,7 +1677,7 @@ bom {
 			]
 		}
 	}
-	library("Spring Data Bom", "2021.2.0") {
+	library("Spring Data Bom", "2021.2.1-SNAPSHOT") {
 		prohibit("[2022.0.0-M1,)") {
 			because "it uses Spring Framework 6"
 		}