dashboard: disable pkgsite for pre-1.21 android builders

The pkgsite tests need CL 472096, released in 1.21 to run properly.
Don't run them on 1.20 and earlier.

For golang/go#59347
For golang/go#61209

Change-Id: I32ba9652401db3b1fb9f23c9777e4514332abaef
Reviewed-on: https://go-review.googlesource.com/c/build/+/524947
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Michael Matloob <[email protected]>
Reviewed-by: Bryan Mills <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: matloob

dashboard/builders.go

@@ -2816,6 +2816,9 @@ func init() {
 				b = true
 			case "build", "blog", "talks", "review", "tour", "website":
 				b = false
+			case "pkgsite":
+				// The pkgsite tests need CL 472096, released in 1.21 to run properly.
+				b = atLeastGo1(goBranch, 21)
 			}
 			return b
 		},
@@ -2854,6 +2857,9 @@ func init() {
 				b = true
 			case "build", "blog", "talks", "review", "tour", "website":
 				b = false
+			case "pkgsite":
+				// The pkgsite tests need CL 472096, released in 1.21 to run properly.
+				b = atLeastGo1(goBranch, 21)
 			}
 			return b
 		},