Add test for issue 15435 (nim-lang#19079)

* Add test for issue 15435

Closes nim-lang#15435.

* Specify bug # in comment

Addresses nim-lang#19079 (comment)

tests/sets/t15435.nim

@@ -0,0 +1,29 @@
+# bug #15435
+discard """
+errormsg: "type mismatch: got <set[uint8], set[range 1..5(uint8)]>"
+nimout: '''t15435.nim(28, 13) Error: type mismatch: got <set[uint8], set[range 1..5(uint8)]>
+but expected one of:
+proc `<`[T](x, y: set[T]): bool
+  first type mismatch at position: 2
+  required type for y: set[T]
+  but expression 'x' is of type: set[range 1..5(uint8)]
+20 other mismatching symbols have been suppressed; compile with --showAllMismatches:on to see them
+
+expression: {1'u8, 5} < x'''
+"""
+
+
+
+
+
+
+## line 20
+var
+  x: set[range[1u8..5u8]]
+
+x.incl(1)
+x.incl(3)
+x.incl(5)
+
+if {1u8, 5} < x:
+  echo "successful"