MSRV change in a patch release

[Eugeny]

error: cannot install package `cargo-deny 0.18.4`, it requires rustc 1.88.0 or newer, while the currently active rustc version is 1.85.0-nightly
`cargo-deny 0.18.3` supports rustc 1.85.0

[AryzXploit]

Raising the MSRV from 1.85 → 1.88 in a patch release (0.18.3 → 0.18.4) breaks users on older toolchains.
Patch releases are expected to stay backward compatible, so this change should ideally go into a new minor/major release instead.