mono-env.eclass: add global-scope ewarn for deprecated < EAPI 7

Signed-off-by: Sam James <sam@gentoo.org>

eclass/mono-env.eclass

@@ -1,4 +1,4 @@
-# Copyright 1999-2023 Gentoo Authors
+# Copyright 1999-2024 Gentoo Authors
 # Distributed under the terms of the GNU General Public License v2
 
 # @ECLASS: mono-env.eclass
@@ -9,14 +9,18 @@
 # @DESCRIPTION:
 # Set environment variables commonly used by dotnet packages.
 
-case ${EAPI} in
-	6|7) ;;
-	*) die "${ECLASS}: EAPI ${EAPI:-0} not supported" ;;
-esac
-
 if [[ -z ${_MONO_ENV_ECLASS} ]] ; then
 _MONO_ENV_ECLASS=1
 
+case ${EAPI} in
+	6)
+		ewarn "${CATEGORY}/${PF}: ebuild uses ${ECLASS} with deprecated EAPI ${EAPI}!"
+		ewarn "${CATEGORY}/${PF}: Support will be removed on 2024-10-08. Please port to newer EAPI."
+		;;
+	7|8) ;;
+	*) die "${ECLASS}: EAPI ${EAPI:-0} not supported" ;;
+esac
+
 SRC_URI="http://download.mono-project.com/sources/${PN}/${P}.tar.bz2"
 
 mono-env_pkg_setup() {