www/py-httpx-sse: Update to 0.4.3

ChangeLog:

• https://github.com/florimondmanca/httpx-sse/releases/tag/0.4.1
• https://github.com/florimondmanca/httpx-sse/releases/tag/0.4.2
• https://github.com/florimondmanca/httpx-sse/releases/tag/0.4.3

Reported by: repology.org