chore: Fix some violations of 'needless_pass_by_ref_mut' lint (#18795)

While this lint is allow-by-default, it seems pretty useful to get rid
of mutable borrows when they're not needed.

Closes #ISSUE

Release Notes:

- N/A

crates/git_hosting_providers/src/git_hosting_providers.rs

@@ -8,7 +8,7 @@ use gpui::AppContext;
 pub use crate::providers::*;
 
 /// Initializes the Git hosting providers.
-pub fn init(cx: &mut AppContext) {
+pub fn init(cx: &AppContext) {
     let provider_registry = GitHostingProviderRegistry::global(cx);
 
     // The providers are stored in a `BTreeMap`, so insertion order matters.