fix: remove whitespaces from doctest names

[lowr]

When rustdoc runs doctests, it removes whitespaces from the tests' path (code). See rust-lang/rust#89422 for details.

Interestingly enough, "Run doctest" has been working without much problem even though rust-analyzer hasn't followed the change. This is because cargo passes the test name to rustdoc via --test-args option, and then rustdoc splits it by whitespace; the last element of the split test name always matches the test name that rustdoc generates.

However, it may run other tests unexpectedly (to be precise, this has long since been a thing because of the split). Consider the following example:

struct A<T, U>(T, U);
struct B<T, U>(T, U);
/// ```
/// doctest here
/// ```
impl<T, U> A<T, U> {}
/// ```
/// doctest here
/// ```
impl<T, U> B<T, U> {}

When you "Run doctest" either of the two, rustdoc considers "U>" one of the test specs and both doctests are run. This patch fixes it by following rustdoc and removing the whitespace from the doctests' name.

[Veykril]

Thanks!
@bors r+

[bors]

📌 Commit d40ab66 has been approved by Veykril

It is now in the queue for this repository.

[bors]

⌛ Testing commit d40ab66 with merge 5edbdd1...

[bors]

☀️ Test successful - checks-actions
Approved by: Veykril
Pushing 5edbdd1 to master...