Use underscore names in setup.cfg

Fixes two build-time warnings from setuptools, each repeated twice:

/tmp/build-env-7f8vloah/lib/python3.12/site-packages/setuptools/dist.py:599: SetuptoolsDeprecationWarning: Invalid dash-separated key 'install-script' in 'bdist_rpm' (setup.cfg), please use the underscore name 'install_script' instead.
!!

        ********************************************************************************
        Usage of dash-separated 'install-script' will not be supported in future
        versions. Please use the underscore name 'install_script' instead.

        Available configuration options are listed in:
        https://setuptools.pypa.io/en/latest/userguide/declarative_config.html

        This deprecation is overdue, please update your project and remove deprecated
        calls to avoid build errors in the future.

        See pypa/setuptools#5011 for details.
        ********************************************************************************

!!
  opt = self._enforce_underscore(opt, section)
/tmp/build-env-7f8vloah/lib/python3.12/site-packages/setuptools/dist.py:599: SetuptoolsDeprecationWarning: Invalid dash-separated key 'post-install' in 'bdist_rpm' (setup.cfg), please use the underscore name 'post_install' instead.
!!

        ********************************************************************************
        Usage of dash-separated 'post-install' will not be supported in future
        versions. Please use the underscore name 'post_install' instead.

        Available configuration options are listed in:
        https://setuptools.pypa.io/en/latest/userguide/declarative_config.html

        This deprecation is overdue, please update your project and remove deprecated
        calls to avoid build errors in the future.

        See pypa/setuptools#5011 for details.
        ********************************************************************************

!!
  opt = self._enforce_underscore(opt, section)

Author: Gedminas, Marius

setup.cfg

@@ -1,7 +1,7 @@
 [bdist_rpm]
 doc_files = README.md AUTHORS COPYING INSTALL.md
-install-script = scripts/rpm-install.sh
-post-install = scripts/rpm-post-install.sh
+install_script = scripts/rpm-install.sh
+post_install = scripts/rpm-post-install.sh
 requires = /usr/bin/python3
     python3-django >= 4.2.20
     python3-django-taggit