Adjust expected errors for a `rustdoc` test

`pulldown-cmark` has slightly different behavior between 0.11.0 and
0.11.2, causing one of the `unportable-markdown` tests to no longer emit
an error. Per [1], remove the error annotation and bless the output.

[1]: https://github.com/rust-lang/rust/pull/128722#issuecomment-2295522292

tests/rustdoc-ui/unportable-markdown.rs

@@ -19,7 +19,6 @@ pub struct GfmFootnotes;
 /// <https://github.com/pulldown-cmark/pulldown-cmark/pull/773>
 ///
 /// test [^foo][^bar]
-//~^ ERROR unportable markdown
 ///
 /// [^foo]: test
 /// [^bar]: test2

tests/rustdoc-ui/unportable-markdown.stderr

@@ -1,31 +1,15 @@
 error: unportable markdown
-  --> $DIR/unportable-markdown.rs:21:10
+  --> $DIR/unportable-markdown.rs:48:5
-   |
-LL | /// test [^foo][^bar]
-   |          ^^^^^^
-   |
-   = help: confusing footnote reference and link
-note: the lint level is defined here
-  --> $DIR/unportable-markdown.rs:8:9
-   |
-LL | #![deny(rustdoc::unportable_markdown)]
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-help: if it should not be a footnote, escape it
-   |
-LL | /// test \[^foo][^bar]
-   |          +
-help: if the footnote is intended, add a space
-   |
-LL | /// test [^foo] [^bar]
-   |                +
-
-error: unportable markdown
-  --> $DIR/unportable-markdown.rs:49:5
    |
 LL | /// >bar
    |     ^
    |
    = help: confusing block quote with no space after the `>` marker
+note: the lint level is defined here
+  --> $DIR/unportable-markdown.rs:8:9
+   |
+LL | #![deny(rustdoc::unportable_markdown)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 help: if the quote is intended, add a space
    |
 LL | /// > bar
@@ -35,5 +19,5 @@ help: if it should not be a quote, escape it
 LL | /// \>bar
    |     +
 
-error: aborting due to 2 previous errors
+error: aborting due to 1 previous error