chore: upgrade httpx to 0.28.1#5

mulka wants to merge 1 commit intoActiveCampaign:mainActiveCampaign/postmark-python:mainfrom

mulka:feature/upgrade-httpx-13djp20hqxpxlmulka/postmark-python:feature/upgrade-httpx-13djp20hqxpxlCopy head branch name to clipboard