Fix .env.toml paths (#15645)

This PR fixes the `.env.toml` paths, since we inadvertently broke them
in https://github.com/zed-industries/zed/pull/15557.

There's likely a better way we can do this, but I wanted to restore the
previous behavior, for now.

Release Notes:

- N/A

crates/collab/src/bin/dotenv.rs

@@ -1,7 +1,7 @@
 use collab::env::get_dotenv_vars;
 
 fn main() -> anyhow::Result<()> {
-    for (key, value) in get_dotenv_vars()? {
+    for (key, value) in get_dotenv_vars(".")? {
         println!("export {}=\"{}\"", key, value);
     }
     Ok(())