Prepare release branch

* disable post-merge benchmarks
* use fixed mx version
* use release overlay

Author: gilles-duboscq

ci.jsonnet

@@ -6,7 +6,7 @@ local common = import 'common.jsonnet';
   // Used to run fewer jobs
   local debug = false,
 
-  local overlay = 'c48d42b13ed07d9bc45ea8cd4d6d6f85c9ff2370',
+  local overlay = 'a36d8fd53fe9941f8c0f7d598baae49d6ed760c3',
 
   local no_overlay = 'cb733e564850cd37b685fcef6f3c16b59802b22c',
 

common.jsonnet

@@ -16,7 +16,7 @@ local jdks = (import "common.json").jdks;
   deploy:      {targets+: ['deploy']},
   gate:        {targets+: ['gate']},
   postMerge:   {targets+: ['post-merge']},
-  bench:       {targets+: ['bench', 'post-merge']},
+  bench:       {targets+: ['bench']},
   dailyBench:  {targets+: ['bench', 'daily']},
   weeklyBench: {targets+: ['bench', 'weekly']},
   manualBench: {targets+: ['bench']},
@@ -30,6 +30,7 @@ local jdks = (import "common.json").jdks;
 
   local common = python3 + {
     packages+: {
+      'mx': '5.268.1',
       'pip:pylint': '==1.9.3',
       'pip:ninja_syntax': '==1.7.2',
     },