skip gomod.txtar testscript on Go 1.20

I had forgotten that Go versions before 1.21 cannot parse these files. CI with Go 1.20 reminded me.
mvdan · Dec 27, 2023 · ddd4dc4 · ddd4dc4
1 parent 5249497
commit ddd4dc4
Showing 1 changed file with 2 additions and 0 deletions.
diff --git a/testdata/script/gomod.txtar b/testdata/script/gomod.txtar
@@ -1,5 +1,7 @@
 # Test various edge cases with go.mod files.
 
+[!go1.21] skip 'Go 1.20 or older cannot parse these go.mod files'
+
 exec gofumpt toolchain-stable/a.go
 stdout '//gofumpt:diagnose.* -lang=v1.21'