Use tag instead of seemingly random commit for upstream build repo

tor-versions.json

@@ -31,7 +31,7 @@
     },
     "upstream": {
       "url": "https://gitlab.torproject.org/tpo/applications/tor-browser-build.git",
-      "commit": "b1b4bf77",
+      "commit": "tbb-12.0.6-build1",
       "tor-browser": "12.0.6",
       "libevent": "2.1.7"
     },