Use dnf5 on Fedora 40+

Fixes https://bugzilla.redhat.com/2264535

mock-core-configs/etc/mock/templates/fedora-branched.tpl

@@ -8,7 +8,10 @@ config_opts['chroot_setup_cmd'] = 'install @{% if mirrored %}buildsys-{% endif %
 
 config_opts['dist'] = 'fc{{ releasever }}'  # only useful for --resultdir variable subst
 config_opts['extra_chroot_dirs'] = [ '/run/lock', ]
-config_opts['package_manager'] = 'dnf'
+
+# https://fedoraproject.org/wiki/Changes/BuildWithDNF5 for Fedora 40+
+config_opts['package_manager'] = '{% if releasever|int >= 40 %}dnf5{% else %}dnf{% endif %}'
+
 config_opts['bootstrap_image'] = 'registry.fedoraproject.org/fedora:{{ releasever }}'
 
 config_opts['dnf.conf'] = """

releng/release-notes-next/f40-dnf5.config

@@ -0,0 +1,5 @@
+Per the approved [Fedora 40 change](https://fedoraproject.org/wiki/Changes/BuildWithDNF5),
+[we switched][PR#1332] the default `package_manager` configuration
+for Fedora 40 or newer to `dnf5`.
+This was previously done when Fedora 40 was Rawhide,
+but it [regressed][rhbz#2264535] when Fedora 40 branched.