_content: fix go.dev/play text color
_content: fix go.dev/play text color

The text color in go.dev/play was accidentally set to color-text-subtle
in CL 384874 whereas the correct color is color-text.

Fixes golang/go#51584

Change-Id: I0a512d826bb88dc16db032334350935503724f09
Reviewed-on: https://go-review.googlesource.com/c/website/+/391394
Reviewed-by: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>
Run-TryBot: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>
Trust: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@google.com>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Valentin Deleplace <dc8c63e56c001c451463d6eebb35626a97f9b210@google.com>
Reviewed-by: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>

golang/website,golang/website,golang/website,golang/website,golang/website,golang/website,golang/website