testing/synctest: panics result in wrong test duration

[neild]

When a test function run by synctest.Test panics, the testing package's panic handler incorrectly uses the bubble's clock to record the duration of test functions, resulting in output like:

--- FAIL: TestNewClientServerTest (-801346049.16s)
    --- FAIL: TestNewClientServerTest/synctest (-801346049.16s)
        --- FAIL: TestNewClientServerTest/synctest/h1 (-801346049.16s)
            --- FAIL: TestNewClientServerTest/synctest/h1 (0.00s)
panic: some panic [recovered, repanicked]

[gopherbot]

Change https://go.dev/cl/676695 mentions this issue: testing, testing/synctest: report correct duration after panics