internal/licenses: accept Python-2.0

For golang/go#45095

Change-Id: Iea030936f382535ec82b64f40fe4b4effc2f5d8f
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/303129
Trust: Jonathan Amsterdam <jba@google.com>
Run-TryBot: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Julie Qiu <julie@golang.org>
TryBot-Result: kokoro <noreply+kokoro@google.com>

internal/licenses/licenses.go

@@ -179,6 +179,7 @@ var (
 		"OpenSSL",
 		"OSL-3.0",
 		"PostgreSQL", // TODO: ask legal
+		"Python-2.0",
 		"Unlicense",
 		"UPL-1.0",
 		"Zlib",