cmd/coordinator: relax the set of x-repo builders allowed as slowbots

In CL 342712, functionality was added to build x-repo builders using
slowbots. However, based on the existing precedent this CL limited this
functionality to trybots. There is no reason for this restriction, so
relax the condition to allow any post-submit builder.

Fixes golang/go#52667

Change-Id: Ica54291605982680a5e69a36a27ac96b79bd5346
Reviewed-on: https://go-review.googlesource.com/c/build/+/403675
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Robert Findley <rfindley@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
diff --git a/cmd/coordinator/coordinator.go b/cmd/coordinator/coordinator.go
index 25b71db..d5ba79f 100644
--- a/cmd/coordinator/coordinator.go
+++ b/cmd/coordinator/coordinator.go
@@ -1308,8 +1308,8 @@
 			if testingKnobSkipBuilds {
 				return nil
 			}
-			if !builder.BuildsRepoTryBot(project, branch, branch) {
-				log.Printf("builder %q isn't configured to build %q@%q as a trybot", builder.Name, project, branch)
+			if !builder.BuildsRepoPostSubmit(project, branch, branch) {
+				log.Printf("builder %q isn't configured to build %q@%q", builder.Name, project, branch)
 				return nil
 			}
 			rev, err := getRepoHead(project)