internal/runtime/maps: enable race for map functions in internal/runtime/maps

internal/runtime/maps: enable race for map functions in internal/runtime/maps

For #54766.

Cq-Include-Trybots: luci.golang.try:gotip-linux-amd64-longtest-swissmap
Change-Id: Iebc7f5482299cb7c4ecccc4c2eb46b4bc42c5fc3
Reviewed-on: https://go-review.googlesource.com/c/go/+/616459
Reviewed-by: Keith Randall <khr@google.com>
Auto-Submit: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@golang.org>