distutils-r1.eclass: Skip dep on ${PN} in EPYTEST_PLUGINS

When `EPYTEST_PLUGINS` contains `${PN}`, skip it when adding
dependencies.  This avoids a self-dependency, while making it possible
to easily test pytest plugins themselves without having to append to
`EPYTEST_PLUGINS` locally.

Signed-off-by: Michał Górny <mgorny@gentoo.org>
Part-of: https://github.com/gentoo/gentoo/pull/43007
Signed-off-by: Michał Górny <mgorny@gentoo.org>

eclass/distutils-r1.eclass

@@ -565,6 +565,10 @@ distutils_enable_tests() {
 			_set_epytest_plugins
 			for plugin in "${EPYTEST_PLUGINS[@]}"; do
 				case ${plugin} in
+					${PN})
+						# don't add a dependency on self
+						continue
+						;;
 					pkgcore)
 						plugin=sys-apps/${plugin}
 						;;