Fix enum warning in heimdal

This fixes a clang 19 warning:

crypto/heimdal/lib/krb5/deprecated.c:75:17: error: comparison of different enumeration types ('krb5_keytype' (aka 'enum ENCTYPE') and 'enum krb5_keytype_old') [-Werror,-Wenum-compare]

75 |     if (keytype != KEYTYPE_DES || context->etypes_des == NULL)
   |         ~~~~~~~ ^  ~~~~~~~~~~~

In https://github.com/heimdal/heimdal/commit/3bebbe5323 this was solved
by adding a cast. That commit is rather large, so I'm only applying the
one-liner here.

MFC after: 3 days

(cherry picked from commit 6f25b46721a18cf4f036d041e7e5d275800a00b3)