Added avatar_image as skipped attribute when editing members

refs https://ghost.slack.com/archives/C02G9E68C/p1652126765251419

Frontend tried also passed `avatar_image` as an attribute to the backend, but this field is not editable.

Author: SimonBackx

packages/admin-api-schema/lib/canary/members-edit.json

@@ -25,6 +25,9 @@
             "maxLength": 191,
             "pattern": "^([^,]|$)"
           },
+          "avatar_image": {
+            "strip": true
+          },
           "note": {
             "type": "string",
             "minLength": 0,

packages/admin-api-schema/lib/canary/members-upload.json

@@ -20,6 +20,9 @@
         "maxLength": 191,
         "pattern": "^([^,]|$)"
       },
+      "avatar_image": {
+        "strip": true
+      },
       "note": {
         "type": ["string", "null"],
         "minLength": 0,