build: Fix e2e tests for builds on v0.78

[mofojed]

• The edge version of deephaven-core installs the latest version of deephaven.ui, which is not compatible with this old version of the UI
• Just pin the e2e tests to an older build of core
• Disabled webkit - the tests were flakey, and updating them would require updating playwright which would require updating all snapshots and reverifying them

[mofojed]

Not sure why this is failing e2e. From the logs:

[WebServer] @deephaven/code-studio: failed to load config from /home/runner/work/web-client-ui/web-client-ui/packages/code-studio/vite.config.ts
[WebServer] @deephaven/code-studio: error when starting preview server:
[WebServer] @deephaven/code-studio: TypeError [ERR_INVALID_ARG_TYPE]: The "paths[1]" argument must be of type string. Received undefined

Which seems to indicate that VITE_BUILD_PATH is undefined. Looking at the web-build logs attached to the failed e2e tests, it looks like the .env file that would set this does not exist, or any other "hidden" file. Unsure why those files are not copied over.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 46.41%. Comparing base (882980d) to head (3866213).

Additional details and impacted files

@@              Coverage Diff               @@
##           release/v0.78    #2315   +/-   ##
==============================================
  Coverage          46.41%   46.41%           
==============================================
  Files                676      676           
  Lines              38875    38875           
  Branches            9841     9816   -25     
==============================================
  Hits               18043    18043           
  Misses             20779    20779           
  Partials              53       53           

Flag	Coverage Δ
unit	46.41% <ø> (ø)

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