Use correct tokens in test to represent an enum variant

Unit variant of externally tagged enum cannot be deserialized from the string
token by itself. It is ContentDeserializer + serde_test::Deserializer that makes
this possible, because serde_test::Deserializer produces Content::Str() from
Token::BorrowedStr() and ContentDeserializer produces unit variant from Content::Str().

The following tokens all produces Content::String(variant):
- Token::String(variant)
- Token::Str(variant)
- Token::UnitVariant { variant, .. }

Token::BorrowedStr(variant) produces Content::Str(variant) that was the real purpose to
use it in test in #933. This actually makes this test testing `Content` rather than type itself.

Correct way to represent enum one of:
- [xxxVariant { .. }]
- [Enum { .. }, xxxVariant { variant, .. }]
- [Enum { .. }, String(variant), <variant content>]
- [Enum { .. }, Str(variant), <variant content>]
- [Enum { .. }, BorrowedStr(variant), <variant content>]

test_suite/tests/test_macros.rs

@@ -997,7 +997,9 @@ fn test_internally_tagged_struct_variant_containing_unit_variant() {
             Token::Str("action"),
             Token::Str("Log"),
             Token::Str("level"),
+            Token::Enum { name: "Level" },
             Token::BorrowedStr("Info"),
+            Token::Unit,
             Token::StructEnd,
         ],
     );
@@ -1009,7 +1011,9 @@ fn test_internally_tagged_struct_variant_containing_unit_variant() {
             Token::Str("action"),
             Token::Str("Log"),
             Token::Str("level"),
+            Token::Enum { name: "Level" },
             Token::BorrowedStr("Info"),
+            Token::Unit,
             Token::MapEnd,
         ],
     );
@@ -1019,7 +1023,9 @@ fn test_internally_tagged_struct_variant_containing_unit_variant() {
         &[
             Token::Seq { len: Some(2) },
             Token::Str("Log"),
+            Token::Enum { name: "Level" },
             Token::BorrowedStr("Info"),
+            Token::Unit,
             Token::SeqEnd,
         ],
     );