gnu: heimdal: Apply patch to fix CVE-2022-45142.

Several recent Heimdal releases are affected by the serious vulnerability
CVE-2022-45142, which NIST scored as "7.5 HIGH". [1]

At the time of writing, the upstream developers had not yet cut any releases
post-7.8.0, which is why the patch is being applied here.

The patch was extracted from Helmut Grohne's public vulnerability
disclosure. [2]

[1] https://nvd.nist.gov/vuln/detail/CVE-2022-45142
[2] https://www.openwall.com/lists/oss-security/2023/02/08/1

* gnu/packages/patches/heimdal-CVE-2022-45142.patch: New patch.
* gnu/local.mk (dist_patch_DATA): Register it.
* gnu/packages/kerberos.scm (heimdal)[source]: Apply it.

Signed-off-by: Maxim Cournoyer <maxim.cournoyer@gmail.com>

gnu/packages/kerberos.scm

@@ -179,6 +179,8 @@ After installation, the system administrator should generate keys using
               (sha256
                (base32
                 "0f4dblav859p5hn7b2jdj1akw6d8p32as6bj6zym19kghh3s51zx"))
+              (patches
+               (search-patches "heimdal-CVE-2022-45142.patch"))
               (modules '((guix build utils)))
               (snippet
                '(begin