RPM: fix Copr conditional

The `copr_project` macro doesn't seem to work anymore given that recent
crun builds on podman-next COPR didn't mention the epoch.

Fix this by switching to `copr_username` instead as that's what podman
and the other repos are currently using.

Signed-off-by: Lokesh Mandvekar <lsm5@redhat.com>

rpm/crun.spec

@@ -6,7 +6,7 @@
 %ifarch aarch64 || x86_64
 %global wasm_support 1
 
-%if %{defined copr_project}
+%if %{defined copr_username}
 %define copr_build 1
 %endif