[sonic-package-manager]: Use lowercase 'azure/sonic' in registry resolver test (#4679)

'Azure/sonic' is not a valid lowercase Docker Hub reference; use 'azure/sonic' so test_get_registry_for passes regardless of the docker-image-py version.

Signed-off-by: Lun Yue <17232861+lunyue-ms@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: lunyue-ms

tests/sonic_package_manager/test_registry.py

@@ -9,7 +9,7 @@ def test_get_registry_for():
     resolver = RegistryResolver()
     registry = resolver.get_registry_for('debian')
     assert registry is resolver.DockerHubRegistry
-    registry = resolver.get_registry_for('Azure/sonic')
+    registry = resolver.get_registry_for('azure/sonic')
     assert registry is resolver.DockerHubRegistry
     registry = resolver.get_registry_for('registry-server:5000/docker')
     assert registry.url == 'https://registry-server:5000'