Fix warnings

[Mingun]

• Fix warnings from Tracking Issue for denying trailing semicolons in expression macro bodies rust-lang/rust#79813:

  warning: trailing semicolon in macro used in expression position
    --> src\events\attributes.rs:362:20
      |
  362 |                 }));
      |                    ^
  ...
  443 |             None => attr!(start_key..end_key),
      |                     ------------------------- in this macro invocation
      |
      = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
      = note: for more information, see issue #79813 <https://github.com/rust-lang/rust/issues/79813>
      = note: macro invocations at the end of a block are treated as expressions
      = note: to ignore the value produced by the macro, add a semicolon after the invocation of `attr`
      = note: this warning originates in the macro `attr` (in Nightly builds, run with -Z macro-backtrace for more info)

  Because in the end it's stay non-obvilious that macro return some value, I've moved out the return keyword from the macro.
• Fix a bug introduced in the 8481c44 -- some errors do not propagated to the caller
• Remove unused import
• Some bit of documentation in the deserializer
• Remove excess cfg check -- it was already checked couple lines above.

[dralley]

Could you also fix the CI which is apparently silently broken?

[dralley]

https://github.com/tafia/quick-xml/blob/master/.github/workflows/rust.yml#L18

This

    - name: Run tests (no features)
      run: cargo test
      run: cargo test --no-default-features

needs to become

    - name: Run tests (no features)
      run: |
          cargo test
          cargo test --no-default-features

[dralley]

Notice the green check mark on this PR even though the tests fail to run, I'm pretty sure that's what happened with the other PR as well.

[Mingun]

needs to become

Are you sure? It seems that line

run: cargo test

need to be completely removed

[dralley]

Sure, that's possible too. Maybe the duplicate line was introduced as part of a bad merge conflict resolution. I'm only speaking about what needs to be done to make it parse properly

[tafia]

Thanks! Indeed I blindly followed the green mark on the PR. Seems to be better now.
@Mingun do you mind fixing the last error?

[Mingun]

Yeah, need always to test changes themself... and do not forget to add --all-features 😄

Fixed the last error.

[tafia]

Awesome thanks!