Rollup merge of #69792 - LenaWil:try_reserve_error/impl-error, r=sfackler

Implement Error for TryReserveError

I noticed that the Error trait wasn't implemented for TryReserveError. (#48043)

Not sure if the error messages and code style are 100% correct, it's my first time contributing to the Rust std.

src/libstd/error.rs

@@ -552,6 +552,9 @@ impl Error for char::ParseCharError {
     }
 }
 
+#[unstable(feature = "try_reserve", reason = "new API", issue = "48043")]
+impl Error for alloc::collections::TryReserveError {}
+
 // Copied from `any.rs`.
 impl dyn Error + 'static {
     /// Returns `true` if the boxed type is the same as `T`