syscall: tests: Fix TestSCMCredentials for `unshare -Umc`

src/syscall/creds_test.go

@@ -76,8 +76,10 @@ func TestSCMCredentials(t *testing.T) {
 			if sys, ok := err.(*os.SyscallError); ok {
 				err = sys.Err
 			}
-			if err != syscall.EPERM {
-				t.Fatalf("WriteMsgUnix failed with %v, want EPERM", err)
+			// can get EINVAL instead of EPERM under `unshare -Umc` because uid0 is not mapped and maps to -1
+			// see also https://github.com/golang/go/issues/42525
+			if !(err == syscall.EPERM || err == syscall.EINVAL) {
+				t.Fatalf("WriteMsgUnix failed with %v, want EPERM/EINVAL", err)
 			}
 		}