recommend java 21 instead of 17 (#1559)

src/docs/common/snippets/common-install-graalvm-sdkman.adoc

@@ -1,15 +1,15 @@
 The easiest way to install https://www.graalvm.org[GraalVM] on Linux or Mac is to use https://sdkman.io/[SDKMan.io].
 
 [source, bash]
-.Java 17
+.Java 21
 ----
-sdk install java 17.0.12-graal
+sdk install java 21.0.5-graal
 ----
 
 [source, bash]
-.Java 17
+.Java 21
 ----
-sdk use java 17.0.12-graal
+sdk use java 21.0.5-graal
 ----
 
 For installation on Windows, or for manual installation on Linux or Mac, see the https://www.graalvm.org/latest/docs/getting-started/[GraalVM Getting Started] documentation.
@@ -20,15 +20,15 @@ The previous command installs Oracle GraalVM, which is free to use in production
 Alternatively, you can use the https://github.com/graalvm/graalvm-ce-builds/releases/[GraalVM Community Edition]:
 
 [source, bash]
-.Java 17
+.Java 21
 ----
-sdk install java 17.0.9-graalce
+sdk install java 21.0.2-graalce
 ----
 
 [source, bash]
-.Java 17
+.Java 21
 ----
-sdk use java 17.0.9-graalce
+sdk use java 21.0.2-graalce
 ----