Auto merge of #51319 - Mark-Simulacrum:rollup, r=Mark-Simulacrum

Rollup of 6 pull requests

Successful merges:

 - #51143 (Specify that packed types must derive, not implement, Copy)
 - #51226 (Make Layout's align a NonZeroUsize)
 - #51297 (Fix run button style)
 - #51306 (impl Default for &mut str)
 - #51312 (Clarify the difference between get_mut and into_mut for OccupiedEntry)
 - #51313 (use type name in E0599 enum variant suggestion)

Failed merges:

diff --cc src/librustdoc/html/static/rustdoc.css
Simple merge