Bump testcontainers to 1.21.4 to fix Docker issue

[yashmayya]

• Attempt to fix errors like:

  19:44:52.125 ERROR [DockerClientProviderStrategy] [main] Could not find a valid Docker environment. Please check configuration. Attempted configurations were:
  	UnixSocketClientProviderStrategy: failed with exception BadRequestException (Status 400: {"message":"client version 1.32 is too old. Minimum supported API version is 1.44, please upgrade your client to a newer version"}
  )
  	DockerDesktopClientProviderStrategy: failed with exception NullPointerException (null). Root cause NullPointerException (null)As no valid configuration was found, execution cannot continue.

which were probably caused by the GitHub Actions runner being updated to use a newer Docker engine version (which dropped support for the older Docker API version being used by our version of testcontainers).

• This is a short term fix. We need to move to the more actively maintained 2.x line for testcontainers soon.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 63.21%. Comparing base (76cd3e6) to head (641423d).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #17704      +/-   ##
============================================
+ Coverage     55.65%   63.21%   +7.55%     
- Complexity      721     1499     +778     
============================================
  Files          2479     3179     +700     
  Lines        140445   190696   +50251     
  Branches      22376    29151    +6775     
============================================
+ Hits          78167   120548   +42381     
- Misses        55694    60775    +5081     
- Partials       6584     9373    +2789     

Flag	Coverage Δ
custom-integration1	100.00% <ø> (?)
integration	100.00% <ø> (+100.00%)	⬆️
integration1	100.00% <ø> (?)
integration2	0.00% <ø> (ø)
java-11	63.18% <ø> (+7.58%)	⬆️
java-21	63.17% <ø> (+7.56%)	⬆️
temurin	63.21% <ø> (+7.55%)	⬆️
unittests	63.21% <ø> (+7.55%)	⬆️
unittests1	55.63% <ø> (-0.03%)	⬇️
unittests2	34.04% <ø> (?)

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

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.