modfile: use reflect.TypeFor instead of reflect.TypeOf

For golang/go#60088.

Change-Id: I7c503c5a18aa7c6de1ffc0c5c115e1a588b2a9e6
Reviewed-on: https://go-review.googlesource.com/c/mod/+/709175
Auto-Submit: Sean Liao <sean@liao.dev>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Sean Liao <sean@liao.dev>
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>

Author: cuishuang

modfile/read_test.go

@@ -251,8 +251,8 @@ func (eq *eqchecker) check(v, w interface{}) error {
 }
 
 var (
-	posType      = reflect.TypeOf(Position{})
-	commentsType = reflect.TypeOf(Comments{})
+	posType      = reflect.TypeFor[Position]()
+	commentsType = reflect.TypeFor[Comments]()
 )
 
 // checkValue checks that v and w represent the same parse tree.