chore: bump ehttpc -> 0.4.8

[thalesmg]

Targeting release-50

Fixes https://emqx.atlassian.net/browse/EMQX-9656

See also emqx/ehttpc#45

This fixes a race condition where the remote server would close the connection before or during requests, and, depending on timing, an {error, normal} response would be returned. In those cases, we should just retry the request without using up "retry credits".

Summary

🤖 Generated by Copilot at 207f081

This pull request fixes a race condition in the HTTP client library ehttpc that could cause EMQ X to crash. It updates the ehttpc dependency in mix.exs and adds a changelog entry in changes/ce/fix-10548.en.md.

PR Checklist

Please convert it to a draft if any of the following conditions are not met. Reviewers may skip over until all the items are checked:

• Added tests for the changes
• Changed lines covered in coverage report
• Change log has been added to changes/{ce,ee}/(feat|perf|fix)-<PR-id>.en.md files
• For internal contributor: there is a jira ticket to track this change
• If there should be document changes, a PR to emqx-docs.git is sent, or a jira ticket is created to follow up
• Schema changes are backward compatible

Checklist for CI (.github/workflows) changes

• If changed package build workflow, pass this action (manual trigger)
• Change log has been added to changes/ dir for user-facing artifacts update