go/zodb: Fix _TestPersistentMapListLoad on py3_pickle3

plist is generated to come with str in [0]. On py2 that is bytestring,
while on py3 it is unicode. However were trying to decode it as
bytestring only and so it was failing as

    --- FAIL: TestPersistentMapListLoad/py3_pickle3 (0.73s)
        persistent_x_test.go:82: plist[0]: got string  ; expect str

-> Fix it by using ogórek.AsString helper as suggested by
StrictUnicode=y mode documentation in https://github.com/kisielk/og-rek/commit/b28613c2.

go/zodb/persistent_x_test.go

@@ -41,10 +41,6 @@ func TestPersistentMapListLoad(t *testing.T) {
 	ztestdataReg.RunWithEach(t, _TestPersistentMapListLoad)
 }
 func _TestPersistentMapListLoad(t0 *testing.T, z *ZTestData) {
-	if z.Kind == "py3_pickle3" {
-		t0.Skip("xfail")
-	}
-
 	assert := assert.New(t0)
 
 	tdb := zodb.OpenTestDB(t0, z.Path("data.fs"))
@@ -81,11 +77,7 @@ func _TestPersistentMapListLoad(t0 *testing.T, z *ZTestData) {
 
 	assert.Equal(len(plist.Data), 3)
 	xa := plist.Data[0]
-	__, ok := xa.(pickle.ByteString)
-	if !ok {
-		t.Fatalf("plist[0]: got %T  ; expect str", xa)
-	}
-	a := string(__)
+	a, err := pickle.AsString(xa); X(err)
 	assert.Equal(a, "a")
 
 	assert.Equal(plist.Data[1], int64(1))

[Kirill Smelkov]

.