doc(port_arm_m): fix the release date of v0.3.2

Author: yvt

src/r3_port_arm_m/CHANGELOG.md

@@ -11,7 +11,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 - **Breaking (semver-exempt):** Change the target compiler version to `nightly-2022-11-10`
 
-## [0.3.2] - 2022-03-19
+## [0.3.2] - 2022-08-16
 
 ### Changed