Rollup merge of #104345 - fmease:fix-up-a-fluent-message, r=compiler-errors

Fix up a Fluent message

Fix up a Fluent message which contained arrows `->` after [selectors](https://projectfluent.org/fluent/guide/selectors.html). The original author probably thought that they were required as part of the selector syntax but in reality they were interpreted as literal text and actually showed up in the emitted diagnostic.

This wasn't caught during the diagnostic migration since the branch constructing the diagnostic in question (`rustc_infer::errors::LifetimeMismatchLabels::Normal`) was not exercised by the UI test suite. I've added two more test cases to do so (one testing `LifetimeMismatchLabels::Normal` where `hir_equal == true` and one where `hir_equal == false`).

Diff visualizing the `->` bug (`master` vs `fix-up-a-fluent-message`):

```diff
 error[E0623]: lifetime mismatch
   --> src/test/ui/implied-bounds/hrlt-implied-trait-bounds-guard.rs:39:30
    |
 39 | fn badboi3<'in_, 'out, T>(a: Foo<'in_, 'out, (&'in_ T, &'out T)>, sadness: &'in_ T) {
    |                              ^^^^^^^^^^^^^^^^^-------^^-------^^
    |                              |                |
    |                              |                these two types are declared with different lifetimes...
-   |                              ...but data->  from `a` flows->  into `a` here
+   |                              ...but data from `a` flows into `a` here
```

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