fix: prevent checkpoint modals from closing on their own [ET-116] [ET-120]

[EmilyBonar]

Description

Addresses the bugs from release part here https://github.com/determined-ai/release-party-issues/issues/1594

Test Plan

• Go to the checkpoints table of a single trial experiment
• Click on the flag in the Checkpoint column to open the checkpoint modal
• Switch between browser tabs and confirm that the modal doesn't close
• Test registering checkpoint
• Repeat all tests on the Workloads table on the Overview tab of the same experiment (below metrics graph)
• Repeat all tests by clicking the "Best Checkpoint" card on the Overview tab
• Repeat all tests on the Trials table of a multi trial experiment

Commentary (optional)

Checklist

• Changes have been manually QA'd
• User-facing API changes need the "User-facing API Change" label.
• Release notes should be added as a separate file under docs/release-notes/.
  See Release Note for details.
• Licenses should be included for new code which was copied and/or modified from any external code.

Ticket

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[codecov]

Codecov Report

Attention: Patch coverage is 11.76471% with 180 lines in your changes are missing coverage. Please review.

Project coverage is 40.12%. Comparing base (3f2d6ab) to head (0e73d40).
Report is 7 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9094      +/-   ##
==========================================
- Coverage   47.06%   40.12%   -6.95%     
==========================================
  Files        1154      831     -323     
  Lines      142378   102998   -39380     
  Branches     2423     2387      -36     
==========================================
- Hits        67006    41324   -25682     
+ Misses      75182    61484   -13698     
  Partials      190      190              

Flag	Coverage Δ
harness	?
web	38.16% <11.76%> (-0.80%)	⬇️

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

Files	Coverage Δ
...act/src/pages/TrialDetails/TrialDetailsMetrics.tsx	21.85% <0.00%> (+0.80%)	⬆️
...ebui/react/src/pages/TrialDetails/TrialInfoBox.tsx	45.16% <27.27%> (+13.48%)	⬆️
...i/react/src/components/RegisterCheckpointModal.tsx	20.24% <21.05%> (-53.73%)	⬇️
webui/react/src/hooks/useCheckpointFlow.tsx	28.57% <21.42%> (+2.85%)	⬆️
.../pages/ExperimentDetails/ExperimentCheckpoints.tsx	14.04% <11.53%> (-0.14%)	⬇️
webui/react/src/hooks/useFetchModels.tsx	28.20% <3.57%> (-3.23%)	⬇️
...t/src/pages/TrialDetails/TrialDetailsWorkloads.tsx	18.66% <10.25%> (-0.72%)	⬇️
...t/src/pages/ExperimentDetails/ExperimentTrials.tsx	12.52% <5.88%> (-0.23%)	⬇️

... and 325 files with indirect coverage changes

[johnkim-det]

LGTM