run the TZ test only on Macs

rslib/Makefile

@@ -33,10 +33,8 @@ RUST_TOOLCHAIN := $(shell cat rust-toolchain)
 	rustup component add clippy-preview --toolchain $(RUST_TOOLCHAIN)
 	@touch $@
 
-# set TZ here for the benefit of a single unit test that fails
-# when running in the GitHub workflow.
 .build/check: .build/rs-tools $(ALL_SOURCE)
-	TZ="Australia/Perth" cargo test --lib -- --nocapture
+	cargo test --lib -- --nocapture
 	cargo fmt -- --check
 	cargo clippy -- -D warnings
 	@touch $@

rslib/src/sched.rs

@@ -122,6 +122,9 @@ mod test {
     }
 
     #[test]
+    #[cfg(target_vendor = "apple")]
+    /// On Linux, TZ needs to be set prior to the process being started to take effect,
+    /// so we limit this test to Macs.
     fn test_local_minutes_west() {
         // -480 throughout the year
         std::env::set_var("TZ", "Australia/Perth");