testing: drop unusual characters from TempDir directory name

Only use safe characters of the test name for the os.MkdirTemp pattern.
This currently includes the alphanumeric characters and ASCII
punctuation characters known not to interact with globs.

Fixes #46624

Change-Id: I402c34775b943fed9b97963c52f79245cc16dc1d
Reviewed-on: https://go-review.googlesource.com/c/go/+/326010


Trust: Tobias Klauser <tobias.klauser@gmail.com>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>