Switch ui tests to trybuild

test_suite/tests/ui/enum-representation/content-no-tag.stderr

@@ -3,6 +3,3 @@ error: #[serde(tag = "...", content = "...")] must be used together
   |
 4 | #[serde(content = "c")]
   |         ^^^^^^^
-
-error: aborting due to previous error
-

test_suite/tests/ui/enum-representation/internal-tuple-variant.stderr

@@ -3,6 +3,3 @@ error: #[serde(tag = "...")] cannot be used with tuple variants
   |
 6 |     Tuple(u8, u8),
   |     ^^^^^^^^^^^^^
-
-error: aborting due to previous error
-

test_suite/tests/ui/enum-representation/untagged-and-adjacent.stderr

@@ -15,6 +15,3 @@ error: untagged enum cannot have #[serde(tag = "...", content = "...")]
   |
 5 | #[serde(tag = "t", content = "c")]
   |                    ^^^^^^^
-
-error: aborting due to 3 previous errors
-

test_suite/tests/ui/enum-representation/untagged-and-content.stderr

@@ -9,6 +9,3 @@ error: untagged enum cannot have #[serde(content = "...")]
   |
 5 | #[serde(content = "c")]
   |         ^^^^^^^
-
-error: aborting due to 2 previous errors
-

test_suite/tests/ui/enum-representation/untagged-and-internal.stderr

@@ -9,6 +9,3 @@ error: enum cannot be both untagged and internally tagged
   |
 5 | #[serde(tag = "type")]
   |         ^^^
-
-error: aborting due to 2 previous errors
-

test_suite/tests/ui/enum-representation/untagged-struct.stderr

@@ -3,6 +3,3 @@ error: #[serde(untagged)] can only be used on enums
   |
 5 | struct S;
   | ^^^^^^
-
-error: aborting due to previous error
-