INSTALL: fix version number in "Upgrading from"

... in accordance with Porting/release_managers_guide.pod, "Update
INSTALL" for BLEAD-POINT.

Author: mauke

INSTALL

@@ -2665,9 +2665,9 @@ seriously consider using a separate directory, since development
 subversions may not have all the compatibility wrinkles ironed out
 yet.
 
-=head2 Upgrading from 5.40.1 or earlier
+=head2 Upgrading from 5.41.9 or earlier
 
-B<Perl 5.41.10 may not be binary compatible with Perl 5.40.1 or
+B<Perl 5.41.10 may not be binary compatible with Perl 5.41.9 or
 earlier Perl releases.>  Perl modules having binary parts
 (meaning that a C compiler is used) will have to be recompiled to be
 used with 5.41.10.  If you find you do need to rebuild an extension with