fix(test): restore #[serial] markers the fallback runner still needs (#6767)

crates/scanner/src/sleeper.rs

@@ -258,6 +258,7 @@ impl SleepTimer {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use serial_test::serial;
     use temp_env::{with_var, with_var_unset};
 
     struct ScannerDefaultSpeedGuard;
@@ -325,6 +326,7 @@ mod tests {
     }
 
     #[test]
+    #[serial]
     fn test_refresh_from_env_applies_speed_and_idle_mode_for_next_cycle() {
         let prev_mode = SCANNER_IDLE_MODE.load(Ordering::Relaxed);
         SCANNER_IDLE_MODE.store(true, Ordering::Relaxed);
@@ -344,6 +346,7 @@ mod tests {
     }
 
     #[test]
+    #[serial]
     fn test_refresh_from_env_uses_default_speed_override_when_speed_unset() {
         let _guard = ScannerDefaultSpeedGuard::set(ScannerSpeed::Slowest);
         let s = DynamicSleeper::new(ScannerSpeed::Default);
@@ -359,6 +362,7 @@ mod tests {
     }
 
     #[tokio::test(start_paused = true)]
+    #[serial]
     async fn test_fastest_never_sleeps() {
         let prev_mode = SCANNER_IDLE_MODE.load(Ordering::Relaxed);
         SCANNER_IDLE_MODE.store(true, Ordering::Relaxed);
@@ -372,6 +376,7 @@ mod tests {
     }
 
     #[tokio::test(start_paused = true)]
+    #[serial]
     async fn test_idle_mode_off_skips_sleep() {
         let prev_mode = SCANNER_IDLE_MODE.load(Ordering::Relaxed);
         SCANNER_IDLE_MODE.store(false, Ordering::Relaxed);