gradle: 7-rc-2 -> 7, bumping latest 6.8.3 -> 7

pkgs/development/tools/build-managers/gradle/default.nix

···
     };
   };
 
-  # NOTE: Gradle 7 is a release candidate, so point to 6.8.
-  gradle_latest = gradle_6_8;
+  gradle_latest = gradle_7;
 
   gradle_7 = gradleGen (gradleSpec {
-    version = "7.0-rc-2";
+    version = "7.0";
     nativeVersion = "0.22-milestone-11";
-    sha256 = "0gzvigyvwwizx90vnzhdnbm5rdaki11inxna11s4y67xkn8hrnx5";
+    sha256 = "01f3bjn8pbpni8kmxvx1dpwpf4zz04vj7cpm6025n0k188c8k2zb";
   });
 
   gradle_6_8 = gradleGen (gradleSpec {