Build error with no_std

[LPGhatguy]

cargo build --no-default-features results in a build error:

error[E0433]: failed to resolve: use of undeclared crate or module `std`
   --> src\lib.rs:254:34
    |
254 |             let key = match std::str::from_utf8(key) {
    |                                  ^^^ not found in `std`
    |
help: consider importing this builtin type
    |
32  | use core::primitive::str;
    |
help: if you import `str`, refer to it directly
    |
254 -             let key = match std::str::from_utf8(key) {
254 +             let key = match str::from_utf8(key) {

A workflow should be added to test no-std to catch regressions like this in the future.