CI: kill lingering Windows smoke-test processes before Publish Log Files (#316173)

After Windows smoke tests finish, Electron child processes (ptyHost,
sharedProcess, network-shared, etc.) can outlive the main process and
keep .build/logs/smoke-tests-electron/*/main.log and friends locked.
That makes the 1ES auto-injected 'Publish Log Files' output fail when
it tries to hash those files (~2 minutes later), failing the whole
Windows Electron Tests job even though all tests passed.

Add a defensive cleanup step right after PublishTestResults that
force-kills any process whose executable lives under the test build
directory, so the publish step has unlocked files to hash.

Refs flaky-test occurrence in build 438755 attempt #1.