fix the forgotten + symbol in parse_ability_result(...) in parser.py

[cyrus-hawk]

Background

The + symbol is forgotten in parse_ability_result(...) func inside parser.py.

Changes

Puts back the + symbol in its place.

Documentation

NA

Test Plan

NA

PR Quality Checklist

• My pull request is atomic and focuses on a single change.
• I have thoroughly tested my changes with multiple different prompts.
• I have considered potential risks and mitigations for my changes.
• I have documented my changes clearly and comprehensively.
• I have not snuck in any "extra" small tweaks changes.
• I have run the following commands against my code to ensure it passes our linters:

  black .
  isort .
  mypy
  autoflake --remove-all-unused-imports --recursive --ignore-init-module-imports --ignore-pass-after-docstring autogpt tests --in-place

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