fix(bigquery): create/update an isolated dataset for collation feature (

#7256)

Resolves flaky tests from https://togithub.com/googleapis/google-cloud-go/issues/7254

bigquery/dataset_integration_test.go

@@ -233,29 +233,47 @@ func TestIntegration_DatasetUpdateDefaultCollation(t *testing.T) {
 	if client == nil {
 		t.Skip("Integration tests skipped")
 	}
+	caseInsensitiveCollation := "und:ci"
+	caseSensitiveCollation := ""
+
 	ctx := context.Background()
-	_, err := dataset.Metadata(ctx)
+	ds := client.Dataset(datasetIDs.New())
+	err := ds.Create(ctx, &DatasetMetadata{
+		DefaultCollation: caseSensitiveCollation,
+	})
 	if err != nil {
 		t.Fatal(err)
 	}
-	caseInsensitiveCollation := "und:ci"
-	// Set the default collation
-	md, err := dataset.Update(ctx, DatasetMetadataToUpdate{
+	md, err := ds.Metadata(ctx)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if md.DefaultCollation != caseSensitiveCollation {
+		t.Fatalf("got %q, want %q", md.DefaultCollation, caseSensitiveCollation)
+	}
+
+	// Update the default collation
+	md, err = ds.Update(ctx, DatasetMetadataToUpdate{
 		DefaultCollation: caseInsensitiveCollation,
 	}, "")
 	if err != nil {
 		t.Fatal(err)
 	}
 	if md.DefaultCollation != caseInsensitiveCollation {
-		t.Fatalf("got %q, want und:ci", md.DefaultCollation)
+		t.Fatalf("got %q, want %q", md.DefaultCollation, caseInsensitiveCollation)
 	}
+
 	// Omitting DefaultCollation doesn't change it.
-	md, err = dataset.Update(ctx, DatasetMetadataToUpdate{Name: "xyz"}, "")
+	md, err = ds.Update(ctx, DatasetMetadataToUpdate{Name: "xyz"}, "")
 	if err != nil {
 		t.Fatal(err)
 	}
 	if md.DefaultCollation != caseInsensitiveCollation {
-		t.Fatalf("got %q, want und:ci", md.DefaultCollation)
+		t.Fatalf("got %q, want %q", md.DefaultCollation, caseInsensitiveCollation)
+	}
+
+	if err := ds.Delete(ctx); err != nil {
+		t.Fatalf("deleting dataset %v: %v", ds, err)
 	}
 }