Auto merge of #28573 - Bryce-MW:warnings-fix, r=jdm

Fix compiler warnings

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While working on my other pull request, I noticed that there were a few compiler warnings that are easy to fix since they simply note some deprecated syntax that can be fixed with no semantic difference. I decided to quickly fix them and submit a PR.

There was also one place where an allowance of unsafe code was not being applied to the correct thing in `components/script/dom/cssrulelist.rs`. It was being applied to a macro `unsafe_no_jsmanaged_fields!` which does contain unsafe code. My understanding (and what the compiler warning states) is that applying that annotation to a macro does nothing even if the macro contains unsafe code. So what I have done is moved this annotation to apply to the entire file. I do not know if that is even necessary since the macro definition is in another file. It would be good to know since it would be best to not add extra allowances when they aren't needed. The compiler warning is below if that helps:
```
warning: unused attribute `allow`
  --> components/script/dom/cssrulelist.rs:24:1
   |
24 | #[allow(unsafe_code)]
   | ^^^^^^^^^^^^^^^^^^^^^
   |
   = note: `#[warn(unused_attributes)]` on by default
note: the built-in attribute `allow` will be ignored, since it's applied to the macro invocation `unsafe_no_jsmanaged_fields`
  --> components/script/dom/cssrulelist.rs:25:1
   |
25 | unsafe_no_jsmanaged_fields!(RulesSource);
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^
```

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- [X] These changes do not require tests because they fix compiler warnings in a way that does not change semantics except as noted.

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