Ralph[m]: confirmed: it is a regression

```
$ cargo --version
cargo 1.88.0 (873a06493 2025-05-10)
$ cargo run --release
    Finished `release` profile [optimized] target(s) in 0.64s
     Running `elf2uf2-rs -d 'target\thumbv6m-none-eabi\release\firmware'`
Found pico uf2 disk F:\
Transfering program to pico
$ rustup toolchain install 1.89
# ...
$ rustup target add --toolchain=1.89 thumbv6m-none-eabi
# ...
$ cargo +1.89 run --release
# [..]
     Running `elf2uf2-rs -d 'target\thumbv6m-none-eabi\release\firmware'`
Found pico uf2 disk F:\
Error: "Unrecognized ABI"
error: process didn't exit successfully: `elf2uf2-rs -d 'target\thumbv6m-none-eabi\release\firmware'` (exit code: 1)
```