add azure-mgmt-mixedreality back into the configuration. verified in build against branch check-acr

Author: scbedd

ci-configs/packages-preview.json

@@ -1038,6 +1038,20 @@
         "prefer_source_distribution": "true",
         "version": ">=12.4.0b1"
       }
+    },
+    {
+      "package_info": {
+        "install_type": "pypi",
+        "prefer_source_distribution": "true",
+        "name": "azure-mgmt-mixedreality",
+        "version": "1.0.0"
+      },
+      "exclude_path": [
+        "test*",
+        "example*",
+        "sample*",
+        "doc*"
+      ]
     }
   ],
   "required_packages": [