ci: swap to cargo fmt nightly

[NexVeridian]

cargo fmt
Warning: can't set `wrap_comments = true`, unstable features are only available in nightly channel.
Warning: can't set `comment_width = 80`, unstable features are only available in nightly channel.
Warning: can't set `format_strings = true`, unstable features are only available in nightly channel.
Warning: can't set `imports_granularity = Crate`, unstable features are only available in nightly channel.
Warning: can't set `group_imports = StdExternalCrate`, unstable features are only available in nightly channel.
Warning: can't set `wrap_comments = true`, unstable features are only available in nightly channel.
Warning: can't set `comment_width = 80`, unstable features are only available in nightly channel.
Warning: can't set `format_strings = true`, unstable features are only available in nightly channel.
Warning: can't set `imports_granularity = Crate`, unstable features are only available in nightly channel.
Warning: can't set `group_imports = StdExternalCrate`, unstable features are only available in nightly channel.
Warning: can't set `wrap_comments = true`, unstable features are only available in nightly channel.
Warning: can't set `comment_width = 80`, unstable features are only available in nightly channel.
Warning: can't set `format_strings = true`, unstable features are only available in nightly channel.
Warning: can't set `imports_granularity = Crate`, unstable features are only available in nightly channel.
Warning: can't set `group_imports = StdExternalCrate`, unstable features are only available in nightly channel.
Warning: can't set `wrap_comments = true`, unstable features are only available in nightly channel.
Warning: can't set `comment_width = 80`, unstable features are only available in nightly channel.
Warning: can't set `format_strings = true`, unstable features are only available in nightly channel.
Warning: can't set `imports_granularity = Crate`, unstable features are only available in nightly channel.
Warning: can't set `group_imports = StdExternalCrate`, unstable features are only available in nightly channel.
Warning: can't set `wrap_comments = true`, unstable features are only available in nightly channel.
Warning: can't set `comment_width = 80`, unstable features are only available in nightly channel.
Warning: can't set `format_strings = true`, unstable features are only available in nightly channel.
Warning: can't set `imports_granularity = Crate`, unstable features are only available in nightly channel.
Warning: can't set `group_imports = StdExternalCrate`, unstable features are only available in nightly channel.
Warning: can't set `wrap_comments = true`, unstable features are only available in nightly channel.
Warning: can't set `comment_width = 80`, unstable features are only available in nightly channel.
Warning: can't set `format_strings = true`, unstable features are only available in nightly channel.
Warning: can't set `imports_granularity = Crate`, unstable features are only available in nightly channel.
Warning: can't set `group_imports = StdExternalCrate`, unstable features are only available in nightly channel.
Warning: can't set `wrap_comments = true`, unstable features are only available in nightly channel.
Warning: can't set `comment_width = 80`, unstable features are only available in nightly channel.
Warning: can't set `format_strings = true`, unstable features are only available in nightly channel.
Warning: can't set `imports_granularity = Crate`, unstable features are only available in nightly channel.
Warning: can't set `group_imports = StdExternalCrate`, unstable features are only available in nightly channel.

[NexVeridian]

since 9014f21 and 8f530f3
steps [rustfmt, clippy] get combined into style

so this pr now runs nightly on both fmt and clippy

to run nightly on only fmt, they will probably need to be uncombined