fix: Change timer font to monospace

[lyndsiWilliams]

SUMMARY

This PR changes the timer to use a monospace font so its width doesn't change.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

BEFORE:

AFTER:

TESTING INSTRUCTIONS

• Go to SQL Lab
• Run a query
• Observe that the width of the timer does not change with the monospace font
• Note: This timer also exists in Explore when fetching data for a chart

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[codecov]

Codecov Report

Merging #21876 (4a381c0) into master (b773354) will decrease coverage by 0.02%.
The diff coverage is 65.16%.

❗ Current head 4a381c0 differs from pull request most recent head 6523c4b. Consider uploading reports for the commit 6523c4b to get more accurate results

@@            Coverage Diff             @@
##           master   #21876      +/-   ##
==========================================
- Coverage   66.92%   66.90%   -0.03%     
==========================================
  Files        1805     1805              
  Lines       69074    69082       +8     
  Branches     7378     7378              
==========================================
- Hits        46228    46219       -9     
- Misses      20940    20953      +13     
- Partials     1906     1910       +4     

Flag	Coverage Δ
javascript	53.28% <63.52%> (-0.04%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...s/superset-ui-core/src/components/SafeMarkdown.tsx	66.66% <ø> (ø)
...ackages/superset-ui-core/src/query/types/Column.ts	100.00% <ø> (ø)
...d/packages/superset-ui-core/src/utils/isDefined.ts	100.00% <ø> (ø)
...src/BigNumber/BigNumberWithTrendline/buildQuery.ts	0.00% <0.00%> (ø)
...hart-echarts/src/MixedTimeseries/transformProps.ts	0.00% <0.00%> (ø)
...et-frontend/src/components/MessageToasts/Toast.tsx	78.78% <ø> (ø)
.../explore/components/ExploreViewContainer/index.jsx	53.00% <ø> (ø)
...ls/DndColumnSelectControl/DndAdhocFilterOption.tsx	50.00% <0.00%> (-50.00%)	⬇️
.../controls/DndColumnSelectControl/OptionWrapper.tsx	65.85% <ø> (ø)
...nents/controls/MetricControl/AdhocMetricOption.jsx	77.77% <ø> (ø)
... and 27 more

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[eschutho]

nice!