test: tweak error message for new images error

Author: mvo5

test/test_manifest.py

@@ -153,8 +153,7 @@ def test_manifest_cross_arch_check(tmp_path, build_container):
                 "manifest", "--target-arch=aarch64",
                 f"localhost/{container_tag}"
             ], check=True, capture_output=True, encoding="utf8")
-        assert 'cannot generate manifest: requested container architecture '\
-            'does not match resolved container: "x86_64" !=' in exc.value.stderr
+        assert 'cannot generate manifest: invalid arch: aarch64' in exc.value.stderr
 
 
 def find_rootfs_type_from(manifest_str):