dashboard: add known issues for linux/loong64
dashboard: add known issues for linux/loong64

(This will cause 'greplogs --triage' to filter out this builder by
default.)

Updates golang/go#53116.

Change-Id: Ib238c641b83f6aec3d1fd75933b7d8593313da21
Reviewed-on: https://go-review.googlesource.com/c/build/+/408938
Reviewed-by: Alex Rakoczy <60c6d277a8bd81de7fdde19201bf9c58a3df08f4@golang.org>
Run-TryBot: Bryan Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

golang/build,golang/build,golang/build,golang/build