Non-consecutive duplicate keys don't trigger duplicate key error

[RedEtherbloom]

Describe the bug

Conflicting non-consecutive keybindings in the duplicate key check array in check() don't trigger the duplicate key error.
The Vector that is used for checking key duplication is not sorted, therefore dedup does not spot these.

To Reproduce

• Reproducible using the test data located here: https://github.com/kdheepak/taskwarrior-testdata/

Steps to reproduce the behavior:
Set quit and previous-tab(example conflict) to the same keybinding
or
Execute ignored test in branch RedEtherbloom/taskwarrior-tui/duplicate_key_fix

cargo test -- keyconfig::tests::test_duplicate_key_error --ignored

Environment (please complete the following information):

• Operating System: Linux / NixOS
• Installation: local cargo build
• taskwarrior-tui version: 0.26.3