ci: Use rust 2024 edition's default resolver instead

[Xuanwo]

Which issue does this PR close?

• Closes chore: pin comfy-table to 7.2.1 to respect our MSRV #9501.

Rationale for this change

We previously used resolver=2 to enable feature unification. This functionality is now covered by the new resolver=3. Additionally, resolver=3 is the default for the Rust 2024 edition and includes the valuable feature of MSRV-aware dependency resolution.

I just remove our old resolver=2 pin so we can use the edition's default.

For more context: https://doc.rust-lang.org/nightly/cargo/reference/resolver.html#resolver-versions

What changes are included in this PR?

cargo's resolver

Are these changes tested?

In CI

Are there any user-facing changes?

No

[scovich]

I don't think the newfangled resolver worked? The MSRV job fails -- really ugly formatting?? -- with:

Checking comfy-table v7.2.2\n
error[E0658]: `let` expressions in this position are unstable\n
  --> /usr/local/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/comfy-table-7.2.2/src/utils/arrangement/disabled.rs:21:12\n
   |\n
21 |         if let Some(max_width) = constraint::max(table, &column.constraint, visible_columns)\n
   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n
   |\n
   = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information\n
\n
error[E0658]: `let` expressions in this position are unstable\n
   --> /usr/local/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/comfy-table-7.2.2/src/utils/formatting/content_format.rs:101:12\n
    |\n
101 |         if let Some(lines) = row.max_height\n
    |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n
    |\n
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information\n
\n
For more information about this error, try `rustc --explain E0658`.\n
error: could not compile `comfy-table` (lib) due to 2 previous errors

Either that, or comfy-table-7.2.2 lies about its MSRV?