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/git_ui/src/git_panel.rs

@@ -4779,9 +4779,7 @@ mod tests {
     use super::*;
 
     fn init_test(cx: &mut gpui::TestAppContext) {
-        if std::env::var("RUST_LOG").is_ok() {
-            env_logger::try_init().ok();
-        }
+        zlog::init_test();
 
         cx.update(|cx| {
             let settings_store = SettingsStore::test(cx);

crates/git_ui/src/project_diff.rs

@@ -1347,7 +1347,7 @@ mod tests {
 
     #[ctor::ctor]
     fn init_logger() {
-        env_logger::init();
+        zlog::init_test();
     }
 
     fn init_test(cx: &mut TestAppContext) {