chore: Prepare for Rust edition bump to 2024 (without autofix) (#27791)

Successor to #27779 - in this PR I've applied changes manually, without
futzing with if let lifetimes at all.

Release Notes:

- N/A

crates/collab/src/env.rs

@@ -20,7 +20,7 @@ pub fn get_dotenv_vars(current_dir: impl AsRef<Path>) -> Result<Vec<(String, Str
 
 pub fn load_dotenv() -> Result<()> {
     for (key, value) in get_dotenv_vars("./crates/collab")? {
-        std::env::set_var(key, value);
+        unsafe { std::env::set_var(key, value) };
     }
     Ok(())
 }