internal/ci: use simpler "go get" to pull a version through the proxy

Sometimes, proxy.golang.org flakes with a confusing error:

	server response: not found: cuelang.org/go/cmd/cue@v0.0.0-20230202153442-63749fe7d1fc:
		invalid version: missing cuelang.org/go/cmd/cue/go.mod at revision 63749fe

The error is not our fault, and it looks like some sort of race or
temporary problem on the proxy's side.

It is interesting that it tries to locate a go.mod file inside cmd/cue.
We only need to pull the module through the proxy, not a package,
so doing just that is simpler and may make this edge case failure
less likely to happen in practice.

Signed-off-by: Daniel Martí <mvdan@mvdan.cc>
Change-Id: I18759da21d45f25dc65049cac4c691ea0f9d38b0
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/549384
Unity-Result: CUEcueckoo <cueckoo@cuelang.org>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>
Reviewed-by: Paul Jolly <paul@myitcv.io>

.github/workflows/trybot.yml

@@ -96,7 +96,7 @@ jobs:
           	# avoid stopping too early. We also use a "failed" file as "go get" runs
           	# in a subshell via the pipe.
           	rm -f failed
-          	if ! GOPROXY=https://proxy.golang.org go get cuelang.org/go/cmd/cue@$v; then
+          	if ! GOPROXY=https://proxy.golang.org go get cuelang.org/go@$v; then
           		touch failed
           	fi |& tee output.txt
 

internal/ci/github/trybot.cue

@@ -97,7 +97,7 @@ trybot: _base.#bashWorkflow & {
 				# avoid stopping too early. We also use a "failed" file as "go get" runs
 				# in a subshell via the pipe.
 				rm -f failed
-				if ! GOPROXY=https://proxy.golang.org go get cuelang.org/go/cmd/cue@$v; then
+				if ! GOPROXY=https://proxy.golang.org go get cuelang.org/go@$v; then
 					touch failed
 				fi |& tee output.txt