x/build: add -longcmdgo TryBot

[matloob]

(This issue is inspired by #76768: it's basically longcrypto but for the go command)

We run longtests for CLs affecting files in the cmd/go tree, because many of the cmd/go tests are not run in short mode (for instance because they run builds). But running all the longtests is really slow.

I'd like for us to add a longcmdgo TryBot that runs cmd/go/... tests without -short, but runs the rest of the tests in short mode.

cc @golang/release

[gabyhelp]

Related Issues

• go/build: add -longcrypto TryBot #76768
• x/build: consider opting-in to longtest builders by default for cmd/go changes, if/when they're under 15 min #42661 (closed)
• x/build/cmd/coordinator: include -longtest and -race builders for trybots on release branches #37827
• x/build/cmd/release{,bot}: include long tests in pre-release testing #29252 (closed)
• proposal: cmd/go: add go test -long #34707 (closed)
• x/build: shard and scale the `longtest` SlowBots #37439 (closed)
• x/build/cmd/coordinator: include full set of tests (rather than limited trybot set) when a builder is requested via SlowBots #38279 (closed)
• x/build: add longtest builders for all first class ports #56822 (closed)
• x/build: reduce ambiguity in long test of main Go repo #39054
• x/build: support an x/tools SlowBot for platforms other than linux-amd64 #39201 (closed)

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[mknyszek]

Relevant comment in the -longcrypto request: #76768 (comment).

[gopherbot]

Change https://go.dev/cl/734863 mentions this issue: main.star: bump longtest shard count up from 4 to 8

[mknyszek]

I sent a CL to double the longtest shard count and try to mitigate the "it's slow" part of the problem.