better default handling for getMultiArchInfo

Fixes https://pagure.io/koji/issue/4161

koji/arch.py

@@ -414,7 +414,9 @@ canonArch = getCanonArch()
 # this gets you the "compat" arch of a biarch pair
 
 
-def getMultiArchInfo(arch=canonArch):
+def getMultiArchInfo(arch=None):
+    if arch is None:
+        arch = canonArch
     if arch in multilibArches:
         return multilibArches[arch]
     if arch in arches and arches[arch] != "noarch":

tests/test_api/data/api.json

@@ -2977,11 +2977,11 @@
             "getMultiArchInfo": {
                 "type": "<class 'function'>",
                 "is_function": true,
-                "desc": "(arch='ia32e')",
+                "desc": "(arch=None)",
                 "args": [
                     {
                         "name": "arch",
-                        "default": "'ia32e'"
+                        "default": "None"
                     }
                 ],
                 "varargs": null,