Update dependencies to unblock build

[sunsided]

This piggybacks on #367 to make the MSRV check pass and updates defmt to 0.3.0+.

This is related to rust-lang/rust#113152

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I spent an hour or so trying to find a combination of minimum versions that would satisfy the

cargo +nightly update -Z minimal-versions
cargo check --features=stm32f303xc,usb,rt,can,ld --lib --examples

check but to no avail. It will introduce a combination of proc-macro2 related versions that are incompatible.