test-rust-examples task: Exit with a fixed error

`... || exit $?` doesn't actually work as expected and the exit call
will fail with:

    numeric argument required

because $? is not yet set.

Author: badboy

Makefile

@@ -73,7 +73,7 @@ endif
 test-rust-examples: glean-core/rlb/tests/*.sh ## Run Rust example tests
 	@for file in $^; do \
 		echo "=== $${file} ==="; \
-		./$$file || exit $?; \
+		./$$file || exit 1; \
 	done
 
 test-rust-with-logs: ## Run all Rust tests with debug logging and single-threaded