cmd/trace: skip tests if parsing fails with timestamp error

cmd/trace: skip tests if parsing fails with timestamp error

runtime/trace test already skips tests in case of the timestamp
error.

Moreover, relax TestAnalyzeAnnotationGC test condition to
deal with the inaccuracy caused from use of cputicks in tracing.

Fixes #24081
Updates #16755

Change-Id: I708ecc6da202eaec07e431085a75d3dbfbf4cc06
Reviewed-on: https://go-review.googlesource.com/97757
Run-TryBot: Hyang-Ah Hana Kim <hyangah@gmail.com>
Reviewed-by: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>