build(deps): update discord-py requirement from ~=2.6.3 to ~=2.6.4

Updates the requirements on [discord-py](https://github.com/Rapptz/discord.py) to permit the latest version.
- [Commits](Rapptz/discord.py@v2.6.3...v2.6.4)

---
updated-dependencies:
- dependency-name: discord-py
  dependency-version: 2.6.4
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

requirements.txt

@@ -1,3 +1,3 @@
-discord.py~=2.6.3
+discord.py~=2.6.4
 asyncpg~=0.30.0
 pyyaml~=6.0.2