fix(shell): correctly handle repeated commands in history

[ksaweryr]

Description

This PR fixes a bug that causes the history index to have the wrong value if the command that was just executed is identical to the last entry in history. To reproduce:

1. run ls
2. run id
3. use up arrow and run id
4. use up arrow - the command that gets autofilled should be id but is ls

Related Issues

Changes Made

• Fixed a bug related to the history feature in shell

Testing Performed

• Built successfully on Debian 13
• Tested manually with make qemu
• Ran test suite with make qemu-test
• All tests pass

Checklist

• Code follows project style guidelines
• Comments added for complex logic
• Builds without warnings
• Tested on QEMU