Update defmt to 0.2.3

[Sh3Rm4n]

This upgrade is needed, as defmt 0.2.0 or 0.2.2 in my case is depending on semver 0.11.0 which then depends on pest_derive 1.0.0 which itself can not build with it minimal choosen dependency version for quote 0.3.0

Upgrading defmt updgrades semver to 1.0.0, which itself does not depend on pest_derive anymore, so that bxcan builds again.

This was all build under the dependecy resolution created by:

cargo +nightly update -Z minimal-versions

[jonas-schievink]

bors r+

[bors[bot]]

Timed out.

[jonas-schievink]

bors retry

[bors[bot]]

Build succeeded:

• ci