dashboard: update host-ios-arm64-corellium-ios to match its previous env

In CL 353549 I refactored environment-handling in the buildlet such
that an explicit per-host GOROOT_BOOTSTRAP environment configured in
dashboard/builders.go overrides the latent GOROOT_BOOTSTRAP value on
the host. (The entry in dashboard/builders.go may omit
GOROOT_BOOTSTRAP entirely to defer to the host environment.)

That change caught out a previously-unnoticed configuration mismatch
for the host-ios-arm64-corellium-ios builder: its entry in
dashboard/builders.go indicated
"GOROOT_BOOTSTRAP=/var/mobile/go-ios-arm64-bootstrap",
but (as shown in previous builder logs¹) it was actually using
"GOROOT_BOOTSTRAP=/var/root/go-ios-arm64-bootstrap".

The latter empirically exists on the builder, while the former
does not.

¹https://build.golang.org/log/4da918256e30f3442be7885019dc2d17bc718e0d

For golang/go#33598.

Change-Id: I09e5f83b46f23d5a4744c752fb66fcd4b33e4cff
Reviewed-on: https://go-review.googlesource.com/c/build/+/354752
Trust: Bryan C. Mills <[email protected]>
Run-TryBot: Bryan C. Mills <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>

Author: Bryan C. Mills

dashboard/builders.go

@@ -623,7 +623,7 @@ var Hosts = map[string]*HostConfig{
 		IsReverse:   true,
 		ExpectNum:   3,
 		env: []string{
-			"GOROOT_BOOTSTRAP=/var/mobile/go-ios-arm64-bootstrap",
+			"GOROOT_BOOTSTRAP=/var/root/go-ios-arm64-bootstrap",
 		},
 	},
 	"host-android-arm64-corellium-android": &HostConfig{