test: 393ae00d regressed backends::tests::test_description due to missing flags in Description::new()

393ae00d adds validation of Description::flags, but backends::tests::test_description test wasn't updated to invert the is_valid() condition, or attempt to init the Description with "valid" flags.

$ RUST_BACKTRACE=1 cargo test backends::tests::test_description -v

running 1 test
test backends::tests::test_description ... FAILED

failures:

---- backends::tests::test_description stdout ----
thread 'backends::tests::test_description' panicked at hbm/src/backends.rs:698:9:
assertion failed: desc.is_valid()
stack backtrace:
   0: rust_begin_unwind
             at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/std/src/panicking.rs:652:5
   1: core::panicking::panic_fmt
             at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/core/src/panicking.rs:72:14
   2: core::panicking::panic
             at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/core/src/panicking.rs:146:5
   3: hbm::backends::tests::test_description
             at ./src/backends.rs:698:9
   4: hbm::backends::tests::test_description::{{closure}}
             at ./src/backends.rs:689:26
   5: core::ops::function::FnOnce::call_once
             at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/core/src/ops/function.rs:250:5
   6: core::ops::function::FnOnce::call_once
             at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/core/src/ops/function.rs:250:5
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.