go/test: add a test for issue 48344

This was fixed by https://go-review.googlesource.com/c/go/+/349613
and https://go-review.googlesource.com/c/go/+/349614

Fixes #48344

Change-Id: I4c62109fd34b20566b07fcca87fb3946a5702fef
Reviewed-on: https://go-review.googlesource.com/c/go/+/350309
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Trust: Dan Scales <danscales@google.com>

test/typeparam/issue48344.go

@@ -0,0 +1,26 @@
+// run -gcflags=-G=3
+
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+type G[T any] interface {
+	g()
+}
+
+type Foo[T any] struct {
+}
+
+func (foo *Foo[T]) g() {
+
+}
+
+func f[T any]() {
+	v := []G[T]{}
+	v = append(v, &Foo[T]{})
+}
+func main() {
+	f[int]()
+}