zlog: Replace usages of env_logger in tests with zlog (#31436)

Also fixes:
https://github.com/zed-industries/zed/pull/31400#issuecomment-2908165249

Release Notes:

- N/A *or* Added/Fixed/Improved ...

crates/language/src/buffer_tests.rs

@@ -39,9 +39,7 @@ pub static TRAILING_WHITESPACE_REGEX: LazyLock<regex::Regex> = LazyLock::new(||
 #[cfg(test)]
 #[ctor::ctor]
 fn init_logger() {
-    if std::env::var("RUST_LOG").is_ok() {
-        env_logger::init();
-    }
+    zlog::init_test();
 }
 
 #[gpui::test]