During repository updates & cleanup there can be a short period of time
when repository metadata is not consistent. There may appear an error
like
E: The repository 'https://termux.org/package stable Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
but it may not be clear for some users what can cause the issue.
This commit improves the situation a bit.
