x/tools/cmd/stringer: adjust generics tests

Per the issue below, a lone type parameter is not permitted
on the the RHS of a type declaration, at least for Go 1.18.

Slightly modified the generics tests so that they pass for
now.

For golang/go#45639.

Change-Id: I3c5dc0ff65bfdc268c372e5e3fdfe00a8547f17e
Reviewed-on: https://go-review.googlesource.com/c/tools/+/359274
Trust: Robert Griesemer <[email protected]>
Run-TryBot: Robert Griesemer <[email protected]>
gopls-CI: kokoro <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Peter Weinberger <[email protected]>

Author: griesemer

cmd/stringer/testdata/typeparams/conv2.go

@@ -10,16 +10,20 @@ package main
 
 import "fmt"
 
-type Other[T interface{ ~int | ~uint }] T // Imagine this is in another package.
+// For now, a lone type parameter is not permitted as RHS in a type declaration (issue #45639).
+// type Other[T interface{ ~int | ~uint }] T // Imagine this is in another package.
+type Other int
 
 const (
-	alpha Other[int] = iota
+	// alpha Other[int] = iota
+	alpha Other = iota
 	beta
 	gamma
 	delta
 )
 
-type Conv2 Other[int]
+// type Conv2 Other[int]
+type Conv2 Other
 
 const (
 	Alpha = Conv2(alpha)

cmd/stringer/testdata/typeparams/prime2.go

@@ -11,9 +11,12 @@ package main
 
 import "fmt"
 
-type Likeint[T interface{ ~int | ~uint8 }] T
+// For now, a lone type parameter is not permitted as RHS in a type declaration (issue #45639).
+// type Likeint[T interface{ ~int | ~uint8 }] T
+type Likeint int
 
-type Prime2 Likeint[int]
+// type Prime2 Likeint[int]
+type Prime2 Likeint
 
 const (
 	p2  Prime2 = 2