fix: restore 1.85 MSRV and fix MSRV CI

[LDeakin]

Closes #811

This just avoids using let chains, which were introduced in 1.88 or something.

[kylebarron]

Thanks!

[progval]

I also get this compilation error on 1.85:

error[E0599]: no function or associated item named `from_utf8` found for type `str` in the current scope
   --> src/parse.rs:477:25
    |
477 |         let body = str::from_utf8(&body).unwrap();
    |                         ^^^^^^^^^ function or associated item not found in `str`
    |
help: you are looking for the module in `std`, not the primitive type
    |
477 |         let body = std::str::from_utf8(&body).unwrap();
    |                    +++++

It's in a test, so not a big deal