test(firestore): fix another readtime clamping expectation (#20074)

Author: shollyman

firestore/integration_test.go

@@ -3459,11 +3459,12 @@ func testIntegrationClientReadTime(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	wantReadTime := tm.Truncate(time.Second)
+	wantReadTime := tm.Truncate(time.Microsecond)
 	for _, d := range ds {
-		if !wantReadTime.Equal(d.ReadTime) {
+		gotTrunc := d.ReadTime.Truncate(time.Microsecond)
+		if !wantReadTime.Equal(gotTrunc) {
 			t.Errorf("wanted read time: %v; got: %v",
-				tm.UnixNano(), d.ReadTime.UnixNano())
+				wantReadTime, gotTrunc)
 		}
 	}
 }