Correctly detect that a module is test suite

Instead of relying on module name to start with "test" (which is not
required neither by UnitTest docs nor by implementation) we now inspect
its source code and check if LibPQ UnitTest metadata field is mentioned.

Author: sio

Modules/UnitTest.Discover.pq

@@ -33,12 +33,17 @@ let
     ),
     LooksLikeSuiteWithError = (name, object) =>
         let
-            NameLikeTest = Text.StartsWith(name, Config[Test.Prefix], Comparer.OrdinalIgnoreCase),
+            ModuleFilename = object[Detail][LibPQ][LibPQ.Source], // error record is assumed
+            Read.Text = LibPQ("Read.Text"),
+            ModuleSource = Read.Text(ModuleFilename, true),
+            ModuleIsTestSuite = Text.Contains(ModuleSource, Config[Suite.MetaField]),
             ObjLikeError =
                 Value.Is(object, type record)
                 and Record.FieldCount(object) = 3
                 and Record.FieldNames(object) = {"Reason", "Message", "Detail"},
-            Return = NameLikeTest and ObjLikeError
+            Return = ObjLikeError and ModuleIsTestSuite // Order matters for short circuiting.
+                                                        // ModuleIsTestSuite assumes that
+                                                        // object is an error record
         in
             Return,
     PropagateErrors = (suite) =>