tests: bump graalvm version to 21.2.0

Noticed a warning from GraalVM native-image:

 --initialize-at-build-time without arguments has been deprecated and
 will be removed in GraalVM 22.0.

But am happily ignoring until I have to deal with it!

Author: lread

.github/workflows/native-image-test.yml

@@ -43,7 +43,7 @@ jobs:
     - name: Install GraalVM
       uses: DeLaGuardo/[email protected]
       with:
-        graalvm: '21.1.0'
+        graalvm: '21.2.0'
         java: ${{ matrix.graal-java }}
 
     #

doc/02-developer-guide.adoc

@@ -21,7 +21,7 @@ Automated testing is setup using GraalVM v21 JDK11.
 * Clojure v1.10.1.697 or above for `clojure` command
 ** Note that rewrite-clj v1 itself supports Clojure v1.9 and above
 * Babashka v0.3.7 or above
-* GraalVM v21.1.0 JDK 11 (if you want to run GraalVM native image tests)
+* GraalVM v21.2.0 JDK 11 (if you want to run GraalVM native image tests)
 
 === Windows Notes