perldelta: Fix syntax

Author: thibaultduponchelle

pod/perldelta.pod

@@ -586,6 +586,8 @@ C<0b101.11p-1>) are now documented. This feature was first introduced in perl
 fixes in perl 5.28.0, but it was never formally documented.
 [L<GH #18664|https://github.com/Perl/perl5/issues/18664>]
 
+=back
+
 =head3 L<perlfunc>
 
 =over 4
@@ -875,8 +877,6 @@ versions did not. These will either be enabled by new files in the F<hints/>
 directories, or new subdirectories and F<README> files at the top level of the
 source tree.
 
-=over 4
-
 =head2 Platform-Specific Notes
 
 =over 4