TST: remove xfail after fix

Summary

caosdb-server#264 (closed) has been fixed with caosdb-server!78 (merged)

test/test_select.cpp

@@ -363,9 +363,7 @@ TEST_F(test_select, test_select_property_unit) {
   EXPECT_EQ(query_transaction->GetResultTable().size(), 1);
   for (const auto &row : query_transaction->GetResultTable().GetRows()) {
 
-    // Fails due to https://gitlab.indiscale.com/caosdb/src/caosdb-server/-/issues/264
-    EXPECT_NONFATAL_FAILURE({ EXPECT_EQ(row.GetValue("TestPropDouble.unit").GetAsString(), "m"); },
-                            "TestPropDouble.unit");
+    EXPECT_EQ(row.GetValue("TestPropDouble.unit").GetAsString(), "m");
   }
 }