internal/crashmonitor: prepare for SetCrashOutput signature change

The function is about to get a second parameter.
This shim will be removed later this week.

Updates golang/go#67182

Change-Id: I166adda831979b713d429504b57510506bfdff11
Reviewed-on: https://go-review.googlesource.com/c/telemetry/+/585378
Reviewed-by: Michael Matloob <matloob@golang.org>
Auto-Submit: Alan Donovan <adonovan@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

internal/crashmonitor/crash_go123.go

@@ -7,8 +7,11 @@
 
 package crashmonitor
 
-import "runtime/debug"
+import (
+	"os"
+	"runtime/debug"
+)
 
 func init() {
-	setCrashOutput = debug.SetCrashOutput
+	setCrashOutput = func(f *os.File) error { return debug.SetCrashOutput(f) }
 }