scm: Stop trying to download src arch

This simplifies configuring extra isos to avoid failing on downloading
non-existing images.

Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>
(cherry picked from commit b3a316776e878d56c683c6558316d0c578c65992)

pungi/wrappers/scm.py

@@ -358,6 +358,8 @@ class ContainerImageScmWrapper(ScmBase):
         raise RuntimeError("Containers can only be exported as files")
 
     def export_file(self, scm_root, scm_file, target_dir, scm_branch=None, arch=None):
+        if arch == "src":
+            return
         ARCHES = {"aarch64": "arm64", "x86_64": "amd64"}
         arch = ARCHES.get(arch, arch)
         cmd = [