[Pkg-rust-maintainers] Bug#1053955: rust-toml: please update to v0.7.8

[Peter Green]

> Please update to (at least) newer upstream release v0.7.8.

toml itself is not semver-breaking, but it's closely coupled dependency
toml_edit is.

Relavent parts of the upstream changelog.

> 0.21.0 - 2023-11-06
> Breaking Change
> 
>     Split default-features=false APIs into parse and display features

> 0.20.0 - 2023-09-13
> Compatibility
> 
>     Serialization and deserialization of tuple variants has changed from being an array to being a table with the key being the variant name and the value being the array

0.20->0.21 looks low risk to me, but 0.19->0.20 looks potentially riskier.

With that in mind lets look at the reverse dependencies.

btm - still on 0.19 upstream.
python-maturin - uses 0.21 upstream, did not make any code changes when bumping from 0.19 to 0.21, already broken and not in testing.
rust-cargo - uses 0.20 upstream, did not make any code changes when bumping from 0.19 to 0.20
rust-rstest-test - uses 0.19 upstream, not in testing, no rdeps
rust-trycmd - uses 0.20 upstream

My overall conclusion is that btm is the main blocker. Jonas, btm is one
of your packages, can you work with upstream to prepare and test an update?

Updated versions of toml_edit and toml are availble in experimental for
you to test with.