test/builder: more architectures in build tag

Add more supported build architectures to the standard build tag.
This will check the logic for (un-)supported build architectures
in the builder plugin. If we only have one arch, which is the
requested arch, it will not catch logic errors, that invert the
supported vs requested architectures.

test/unit/test_builder.py

@@ -213,7 +213,7 @@ class TestBuilderPlugin(PluginTest):
         }
 
         build_config = {
-            "arches": "x86_64"
+            "arches": "s390x aarch64 ppc64le x86_64"
         }
 
         repo_info = {