RMG - Make last_version handle smoothly provided RC version numbers

Author: thibaultduponchelle

Porting/make-rmg-checklist

@@ -152,7 +152,8 @@ my $passthru_headers = qr/^= (?: over | item | back | cut )/xms;
 # version used when generating diffs (acknowledgements, Module::CoreList etc)
 # 5.36.0 -> 5.34.0
 # 5.36.1 -> 5.36.0
-my ($major, $minor, $point) = split(/\./, $version);
+my ($major, $minor, $point_with_maybe_rc) = split(/\./, $version);
+my ($point) = split(/-/, $point_with_maybe_rc);
 my $last_version = join('.', $major, ($point == 0 ? ($minor - 2, 0) : ($minor, $point-1)));