Fix cropping of leaderboard sidebar expansion icon

[VasylMarchuk]

Closes #3100

Brief

This bumps the z-index for leaderboard sidebar to fix cropping of expand/collapse button

Screenshot

Checklist

• I've thoroughly self-reviewed my changes
• I've added tests for my changes, unless they affect admin-only areas (or are otherwise not worth testing)
• I've verified any visual changes using Percy (add a commit with [percy] in the message to trigger)

[codecov]

Bundle Report

Changes will decrease total bundle size by 1.62kB (-0.0%) ⬇️. This is within the configured threshold ✅

Detailed changes

Bundle name	Size	Change
client-array-push	38.77MB	-1.62kB (-0.0%) ⬇️

Affected Assets, Files, and Routes:

view changes for bundle: client-array-push

Assets Changed:

Asset Name	Size Change	Total Size	Change (%)
assets/chunk.*.js	5 bytes	395.94kB	0.0%
assets/chunk.*.js	-1.57kB	3.32MB	-0.05%
assets/chunk.*.js	-82 bytes	40.85kB	-0.2%
assets/chunk.*.css	31 bytes	254.87kB	0.01%

[github-actions]

Test Results

678 tests  ±0   627 ✅ ±0   9m 28s ⏱️ -1s
  1 suites ±0    51 💤 ±0 
  1 files   ±0     0 ❌ ±0 

Results for commit b5d3a0c. ± Comparison against base commit 377e270.

♻️ This comment has been updated with latest results.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

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