chore: upgrade vaadin-testbench to 9.3.8

[vaadin-bot]

No description provided.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.65%. Comparing base (933f5e5) to head (67f1c41).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3173   +/-   ##
=======================================
  Coverage   92.65%   92.65%           
=======================================
  Files          85       85           
  Lines        3187     3187           
  Branches      778      778           
=======================================
  Hits         2953     2953           
  Misses        182      182           
  Partials       52       52           

Flag	Coverage Δ
unittests	92.65% <ø> (ø)

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[vaadin-bot]

Hi @vaadin-bot and @cromoteca, when i performed cherry-pick to this commit to 24.5, i have encountered the following issue. Can you take a look and pick it manually?
Error Message:
Error: Command failed: git cherry-pick 854d42e
error: could not apply 854d42e... chore: upgrade vaadin-testbench to 9.3.8 (#3173)
hint: After resolving the conflicts, mark them with
hint: "git add/rm ", then run
hint: "git cherry-pick --continue".
hint: You can instead skip this commit with "git cherry-pick --skip".
hint: To abort and get back to the state before "git cherry-pick",
hint: run "git cherry-pick --abort".