Rollup merge of #80812 - rust-lang:relnotes-1.50.0, r=Mark-Simulacrum
Rollup merge of #80812 - rust-lang:relnotes-1.50.0, r=Mark-Simulacrum

Update RELEASES.md for 1.50.0

### [Rendered](https://github.com/rust-lang/rust/blob/relnotes-1.50.0/RELEASES.md)

r? `@Mark-Simulacrum`
cc `@rust-lang/release`

aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust