community/exim: upgrade to 4.95
It blocks build of 3.15 as only latest version packaged at https://ftp.exim.org/pub/exim/exim4/
the release is regular https://github.com/Exim/exim/blob/exim-4.95/doc/doc-txt/ChangeLog#L6
The current version is 4.95.If necessary, we publish maintenance releases. These releases are mainly intended for package maintainers.