x/pkgsite/internal/xcontext: TestStats failures with MillisToLastByte out of expected range

[gopherbot]

#!watchflakes
post <- pkg == "golang.org/x/pkgsite/internal/xcontext" && test == "TestStats" && `MillisToLastByte is \d+, wanted \d+`

Issue created automatically to collect these failures.

Example (log):

2023/06/29 00:02:26 Info: caching response of length 25 for /A
2023/06/29 00:02:26 Debug: serving "/A" from cache
2023/06/29 00:02:26 Info: caching response of length 25 for /A
2023/06/29 00:02:26 Debug: serving "/A" from cache
2023/06/29 00:02:27 Error: middleware.Panic: panic!
--- FAIL: TestStats (0.59s)
    stats_test.go:72: MillisToLastByte is 587, wanted 500 +/- 50

— watchflakes

[gopherbot]

Found new dashboard test flakes for:

#!watchflakes
default <- pkg == "golang.org/x/pkgsite/internal/xcontext" && test == "TestStats"

2023-06-28 17:58 linux-s390x-ibm pkgsite@a9d9eedc go@03cd8a7b x/pkgsite/internal/xcontext.TestStats (log)

2023/06/29 00:02:26 Info: caching response of length 25 for /A
2023/06/29 00:02:26 Debug: serving "/A" from cache
2023/06/29 00:02:26 Info: caching response of length 25 for /A
2023/06/29 00:02:26 Debug: serving "/A" from cache
2023/06/29 00:02:27 Error: middleware.Panic: panic!
--- FAIL: TestStats (0.59s)
    stats_test.go:72: MillisToLastByte is 587, wanted 500 +/- 50

— watchflakes

[bcmills]

Compare #61273.

[gopherbot]

Found new dashboard test flakes for:

#!watchflakes
post <- pkg == "golang.org/x/pkgsite/internal/xcontext" && test == "TestStats" && `MillisToLastByte is \d+, wanted \d+`

2023-07-31 22:57 linux-s390x-ibm pkgsite@0d6a9589 go@2300f7ef x/pkgsite/internal/xcontext.TestStats (log)

2023/08/01 23:37:19 Info: caching response of length 25 for /A
2023/08/01 23:37:19 Debug: serving "/A" from cache
2023/08/01 23:37:19 Info: caching response of length 25 for /A
2023/08/01 23:37:19 Debug: serving "/A" from cache
2023/08/01 23:37:20 Error: middleware.Panic: panic!
--- FAIL: TestStats (0.71s)
    stats_test.go:72: MillisToLastByte is 706, wanted 500 +/- 50

— watchflakes