Please set default branch to 'main' in codecov.io

Describe the bug

Since we enabled the code coverage using Codecov Getting the error Please upload report for BASE (main@####).

To Reproduce

Just open a PR with any change:

Validate the issue
Click the Codecov badge or visit the site
This will use branch 'master', which is an old codecov result:

How to fix
A project administrator needs to visit https://app.codecov.io/gh/testcontainers/testcontainers-python/settings and change the default branch from 'master' to 'main'. It should look like this:

打开 issue 中 URL 对应的 Codecov 项目设置，检查已配置的默认分支。将其从 master 更改为 main，然后打开一个 pull request，并检查 Codecov 报告和徽章，以确认它们使用的是 main。