e2e tests: use t.Context() from testing as context.Context

[timvaillancourt]

Description

This PR moves instances of context.Background() -> t.Context() in e2e tests

This is a built-in context from the testing package that lets cancellations of go test (CTRL+C) to propagate down to tests

Related Issue(s)

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 69.89%. Comparing base (7a3acd5) to head (89624be).
⚠️ Report is 14 commits behind head on main.

Files with missing lines	Patch %	Lines
go/test/stress/utils.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #19081      +/-   ##
==========================================
- Coverage   69.90%   69.89%   -0.02%     
==========================================
  Files        1612     1612              
  Lines      215817   215817              
==========================================
- Hits       150865   150841      -24     
- Misses      64952    64976      +24     

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[arthurschreiber]

Nice! I was initially concerned about this change introducing backporting pains, but t.Context was added in go 1.24, and given that Vitess 22.x (oldest supported release branch at the time of writing) requires at least 1.24.10, I'm all in favor of this change. 👍