workflow: disable cockroach-microbench-ci

Following the discussions in
cockroachdb#135899. This job is being
disabled until we are able to figure out how to remove the variance in
microbenchmarks cockroachdb#106661

Epic: none

Release note: None

.github/workflows/github-actions-essential-ci.yml

@@ -347,6 +347,7 @@ jobs:
         if: always()
   cockroach-microbench-ci:
     runs-on: [ self-hosted, basic_runner_group ]
+    if: false # TODO(106661): Re-enable this job after fixing variance and false positives
     timeout-minutes: 60
     steps:
       - uses: actions/checkout@v4