gopls/internal/regtest: skip a some new builders where regtests time out

Updates golang/go#42789
Updates golang/go#43355

Change-Id: Ic344237e492b08c30c4d86db6a6a39a561e2d27b
Reviewed-on: https://go-review.googlesource.com/c/tools/+/280092
Run-TryBot: Robert Findley <rfindley@google.com>
Trust: Robert Findley <rfindley@google.com>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Go Bot <gobot@golang.org>

gopls/internal/regtest/runner.go

@@ -323,6 +323,8 @@ var longBuilders = map[string]string{
 	"openbsd-amd64-64":        "golang.org/issues/42789",
 	"openbsd-386-64":          "golang.org/issues/42789",
 	"openbsd-386-68":          "golang.org/issues/42789",
+	"openbsd-amd64-68":        "golang.org/issues/42789",
+	"linux-arm":               "golang.org/issues/43355",
 	"darwin-amd64-10_12":      "",
 	"freebsd-amd64-race":      "",
 	"illumos-amd64":           "",