cmd/compile: assertion failure in validType test [go1.23]

[griesemer]

The following code causes a compiler crash (playground):

package p

import "time"

type S[T any] struct {
	a T
	b time.Time
}

var _ S[time.Time]

panic: /Users/gri/goroot/src/cmd/compile/internal/types2/validtype.go:126: assertion failed [recovered]
        panic: /Users/gri/goroot/src/cmd/compile/internal/types2/validtype.go:126: assertion failed [recovered]
        panic: /Users/gri/goroot/src/cmd/compile/internal/types2/validtype.go:126: assertion failed

[gopherbot]

Change https://go.dev/cl/571836 mentions this issue: go/types, types2: avoid assertio failure in Checker.validType