repos: show x/playground on post-submit dashboard, update dependencies

We enabled post-submit builders for x/playground in golang/go#24823.
Stop marking it as "hidden from the dashboard".

Fixes golang/go#66001.

Change-Id: I96f581aa93ec76748e888c1ad5c50f260beffa59
Reviewed-on: https://go-review.googlesource.com/c/build/+/609140
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
Reviewed-by: Michael Pratt <[email protected]>
Auto-Submit: Dmitri Shuralyov <[email protected]>

Author: dmitshur

repos/repos.go

@@ -84,7 +84,7 @@ func init() {
 	x("perf", desc("packages and tools for performance measurement, storage, and analysis"))
 	x("pkgsite", desc("home of the pkg.go.dev website"), enableCSR("go-discovery"))
 	x("pkgsite-metrics", desc("code for serving pkg.go.dev/metrics"), enableCSR("go-ecosystem"))
-	x("playground", noDash, enableCSR("golang-org"))
+	x("playground", enableCSR("golang-org"))
 	x("review", desc("a tool for working with Gerrit code reviews"))
 	x("scratch", noDash)
 	x("sync", desc("additional concurrency primitives"))