Disable merge on refresh in DiskThresholdDeciderIT

[nknize]

Disables merge on refresh for DiskThresholdDeciderIT.testRestoreSnapshotAllocationDoesNotExceedWatermark. This fixes reproducible failure on main and 2.x branches:

./gradlew ':server:internalClusterTest' --tests "org.opensearch.cluster.routing.allocation.decider.DiskThresholdDeciderIT.testRestoreSnapshotAllocationDoesNotExceedWatermark" -Dtests.seed=926BB9577ACEFB6 -Dtests.security.manager=true -Dtests.jvm.argline="-XX:TieredStopAtLevel=1 -XX:ReservedCodeCacheSize=64m" -Dtests.locale=es-PR -Dtests.timezone=America/Virgin -Druntime.java=17

closes #4162

[reta]

Issue #4162

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: UNSTABLE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/4866/
• CommitID: 4d6efd1

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: UNSTABLE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/4867/
• CommitID: 493a629

[nknize]

#4830

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: SUCCESS ✅
• URL: https://build.ci.opensearch.org/job/gradle-check/4882/
• CommitID: 493a629

[codecov-commenter]

Codecov Report

Merging #4828 (493a629) into main (cdc7a2f) will decrease coverage by 0.01%.
The diff coverage is 50.00%.

@@             Coverage Diff              @@
##               main    #4828      +/-   ##
============================================
- Coverage     70.74%   70.73%   -0.02%     
+ Complexity    57888    57868      -20     
============================================
  Files          4689     4689              
  Lines        277305   277296       -9     
  Branches      40370    40363       -7     
============================================
- Hits         196190   196138      -52     
- Misses        64794    64893      +99     
+ Partials      16321    16265      -56     

Impacted Files	Coverage Δ
...reness/get/GetDecommissionStateRequestBuilder.java	0.00% <0.00%> (ø)
...eness/get/TransportGetDecommissionStateAction.java	23.07% <0.00%> (-1.93%)	⬇️
.../org/opensearch/client/support/AbstractClient.java	32.54% <ø> (ø)
.../admin/cluster/RestGetDecommissionStateAction.java	42.85% <25.00%> (-17.15%)	⬇️
...on/awareness/get/GetDecommissionStateResponse.java	42.85% <47.36%> (-1.92%)	⬇️
...ion/awareness/get/GetDecommissionStateRequest.java	82.35% <83.33%> (+82.35%)	⬆️
...adonly/AddIndexBlockClusterStateUpdateRequest.java	0.00% <0.00%> (-75.00%)	⬇️
...luster/routing/allocation/RoutingExplanations.java	41.37% <0.00%> (-58.63%)	⬇️
...readonly/TransportVerifyShardIndexBlockAction.java	9.75% <0.00%> (-58.54%)	⬇️
.../admin/cluster/reroute/ClusterRerouteResponse.java	55.00% <0.00%> (-45.00%)	⬇️
... and 478 more

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[opensearch-trigger-bot]

The backport to 2.x failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-2.x 2.x
# Navigate to the new working tree
cd .worktrees/backport-2.x
# Create a new branch
git switch --create backport/backport-4828-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 49363fb06a4cbd48e6baa90f53b74764fb8ec155
# Push it to GitHub
git push --set-upstream origin backport/backport-4828-to-2.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-2.x

Then, create a pull request where the base branch is 2.x and the compare/head branch is backport/backport-4828-to-2.x.