use defmt-test in the test suite

Author: japaric

testsuite/tests/test.rs

@@ -4,7 +4,8 @@
 use cortex_m_rt::entry;
 use {{crate_name}} as _; // memory layout + panic handler
 
-// See https://crates.io/crates/defmt-test/0.1.0 for more documentation
+// See https://crates.io/crates/defmt-test/0.1.0 for more documentation (e.g. about the 'state'
+// feature)
 #[defmt_test::tests]
 mod tests {
     #[test]