Backport #20272
Unfortunately it appears that 2048 bit RSA keys can occasionally be created in such
a way that they appear to have 2047 bit length. This PR simply changes our defaults to
allow these.
Fix#20249
Signed-off-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>