Fix chromedp shutdown temporary file race condition

[meln5674]

In some situations, cleanup of an otherwise successful test suite fails with the error

[FAILED] DeferCleanup callback returned error: unlinkat /tmp/ginkgo$RANDOMID/Default: directory not empty

reported to be at

$GOPATH/pkg/mod/github.com/onsi/ginkgo/v2@v2.14.0/internal/testingtproxy/testing_t_proxy.go:153

As best I can tell, this is a result of the spawned chrome instance writing a temporary file after ginkgo attempts to run a DeferCleanup-ed os.Remove on its directory as a result of a race condition.

This patch, at least empirically, fixes this by calling chromedp.Cancel which, according to its docstring, ensures chrome is cleaned up before returning.

As a test, a test suite which would previously fail with this error at a rate of about 1 in 10 was run with --until-it-fails for 10 minutes without error. Removing this line and running again resulted in a failure within a minute.

[onsi]

sweet, thanks!