Recursive `--config-path` doesn't recurse

Describe the bug

The --config-path help description says:

        --config-path [Path for the configuration file]
                        Recursively searches the given path for the
                        rustfmt.toml config file. If not found reverts to the
                        input file path

However it doesn't seem to recurse:

$ rustfmt --config-path ~/Downloads/test_issue/my_crate/src/main.rs --edition 2018 < ~/Downloads/test_issue/my_crate/src/main.rs
Could not parse TOML: expected an equals, found an identifier at line 1 column 4

$ rustfmt --config-path ~/Downloads/test_issue/my_crate/src/ --edition 2018 < ~/Downloads/test_issue/my_crate/src/main.rs
Error: unable to find a config file for the given path: `~/Downloads/test_issue/my_crate/src/`

$ rustfmt --config-path ~/Downloads/test_issue/my_crate/src --edition 2018 < ~/Downloads/test_issue/my_crate/src/main.rs
Error: unable to find a config file for the given path: `~/Downloads/test_issue/my_crate/src`

$ rustfmt --config-path ~/Downloads/test_issue/my_crate --edition 2018 < ~/Downloads/test_issue/my_crate/src/main.rs
fn fjsdlkfjklsdajflksdjlfdasdsadsadsaadkjdskljflkasj_jflksjdklfjsdlkjflkdjslkfjas(a: i32, b: i32, c: i32) {
    println!("TEST");
}

fn main() {
    fjsdlkfjklsdajflksdjlfdasdsadsadsaadkjdskljflkasj_jflksjdklfjsdlkjflkdjslkfjas(1, 2, 3);
    println!("Hello, world!");
}

$ rustfmt --config-path ~/Downloads/test_issue/ --edition 2018 < ~/Downloads/test_issue/my_crate/src/main.rs
Error: unable to find a config file for the given path: `~/Downloads/test_issue/`

To Reproduce

Test project is the one from https://github.com/rust-analyzer/rust-analyzer/issues/6973#issuecomment-762881775

Expected behavior

rustfmt --config-path follows the same logic as rustfmt

Meta

• rustfmt version: rustfmt 1.4.32-nightly (216a643 2021-01-16)
• From where did you install rustfmt?: rustup
• How do you run rustfmt: rustfmt

Start by reproducing the reported --config-path commands against the linked rust-analyzer test project, then trace rustfmt's --config-path handling and its configuration-file search logic. Done means a path beneath a rustfmt.toml location searches recursively and behaves consistently with ordinary rustfmt invocation, while preserving the documented fallback behavior.