internal/ci: fix goreleaser when using gomod.proxy

We enable gomod.proxy, meaning that `goreleaser release` builds CUE tags
by pulling the version through proxy.golang.org, which helps so that
our CUE binaries get stamped with the right main module version.

This unfortunately broke with a recent change adding `id: main`,
which caused the CI build of v0.8.0-alpha.2 to fail:

    failed to proxy module: exit status 1: go: malformed module path "./cmd/cue": invalid path element "."

Paul added the explicit "id" field because otherwise goreleaser
complains about duplicate ID strings:

    found 2 builds with the ID 'cue', please fix your config

It should default to the binary name string, so make it that,
which fixes the build of v0.8.0-alpha.2 with goreleaser.
I verified this with `goreleaser --skip=announce,publish,validate`,
which is similar to `goreleaser --snapshot`, but expects a current tag
and also does keep gomod.proxy enabled.

Leave notes to remind ourselves of the tricky details above.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: I2e65a706601c65e7219c5822727b650fe4225461
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1176868
TryBot-Result: CUEcueckoo <[email protected]>
Reviewed-by: Paul Jolly <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>

internal/ci/goreleaser/goreleaser.cue

@@ -4,6 +4,9 @@ config: {
 	#latest: bool @tag(latest, type=bool)
 
 	project_name: "cue"
+	// Note that gomod.proxy is ignored by `goreleaser release --snapshot`,
+	// which we use in CI to test the goreleaser config and build,
+	// as --snapshot is meant for entirely local builds without a git tag.
 	gomod: proxy: true
 
 	// Template based on common settings
@@ -17,7 +20,9 @@ config: {
 		flags: *[
 			"-trimpath",
 		] | _
-		id:            main
+		// Note that goreleaser says that id defaults to the binary name,
+		// but it then complains about "cue" being duplicate even though we use "cue" and "cuepls".
+		id:            binary
 		main:          string
 		binary:        string
 		mod_timestamp: *'{{ .CommitTimestamp }}' | _