Build the enum-keyed map test object instead of parsing it

ci_test_diagnostic_positions failed in unit-enum_keyed_maps_default.cpp:
with JSON_DIAGNOSTIC_POSITIONS, a parsed value adds its byte range to
the exception message ("(bytes 0-7) type must be array, but is
object"), so the exact-message checks did not match. Build the object
in memory, like unit-custom-array-type.cpp does.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

tests/src/unit-enum_keyed_maps_default.cpp

@@ -122,11 +122,14 @@ TEST_CASE("maps with enum keys")
 
     SECTION("objects are only read for enum keys")
     {
+        // built rather than parsed, so that the messages do not gain a byte
+        // range with JSON_DIAGNOSTIC_POSITIONS
+        const json j = {{"1", 2}};
         int_map im;
         int_umap ium;
-        CHECK_THROWS_WITH_AS(json::parse(R"({"1":2})").get_to(im),
+        CHECK_THROWS_WITH_AS(j.get_to(im),
                              "[json.exception.type_error.302] type must be array, but is object", json::type_error&);
-        CHECK_THROWS_WITH_AS(json::parse(R"({"1":2})").get_to(ium),
+        CHECK_THROWS_WITH_AS(j.get_to(ium),
                              "[json.exception.type_error.302] type must be array, but is object", json::type_error&);
     }