Bump openjdk version from 17 to 21

Bypass-Presubmit-Reason: Tested in louhi

Change-Id: I7a05ca1561eaa532e14a9ad3380721962fa088e0
diff --git a/install-prereqs.sh b/install-prereqs.sh
index f0bbb39..89c60ac 100755
--- a/install-prereqs.sh
+++ b/install-prereqs.sh
@@ -71,8 +71,8 @@
     mono-complete
     ncurses-dev
     ninja-build
-    openjdk-17-jdk-headless
-    openjdk-17-jre-headless
+    openjdk-21-jdk-headless
+    openjdk-21-jre-headless
     perl
     protobuf-compiler
     pv