Avoid an unwrap when loading languages (#8562)

We couldn't reproduce the panic, but I believe it was possible when
uninstalling an extension while one if its grammars was still loading.

Release Notes:
- Fixed a crash that could happen when uninstalling a language extension
while its grammar was loading.

---------

Co-authored-by: Conrad <conrad@zed.dev>

crates/language/src/language.rs

@@ -1522,16 +1522,16 @@ mod tests {
         });
 
         languages
-            .language_for_file("the/script", None)
+            .language_for_file("the/script".as_ref(), None)
             .await
             .unwrap_err();
         languages
-            .language_for_file("the/script", Some(&"nothing".into()))
+            .language_for_file("the/script".as_ref(), Some(&"nothing".into()))
             .await
             .unwrap_err();
         assert_eq!(
             languages
-                .language_for_file("the/script", Some(&"#!/bin/env node".into()))
+                .language_for_file("the/script".as_ref(), Some(&"#!/bin/env node".into()))
                 .await
                 .unwrap()
                 .name()