Bump docfx from 2.67.1 to 2.70.4 (#1336)

Author: dependabot[bot]

.config/dotnet-tools.json

@@ -21,7 +21,7 @@
       ]
     },
     "docfx": {
-      "version": "2.67.1",
+      "version": "2.70.4",
       "commands": [
         "docfx"
       ]