add testcase for #7165 (#15368)

* add testcase for #7165

* Remove overspecific testament spec

Co-authored-by: Clyybber <darkmine956@gmail.com>

tests/distinct/t7165.nim

@@ -0,0 +1,15 @@
+
+type
+  Table[K, V] = object
+    key: K
+    val: V
+
+  MyTable = distinct Table[string, int]
+  MyTableRef = ref MyTable
+
+proc newTable[K, V](): ref Table[K, V] = discard
+
+proc newMyTable: MyTableRef =
+  MyTableRef(newTable[string, int]()) # <--- error here
+
+discard newMyTable()