chore: fix python lint warnings (#14638)

* chore: fix lint warnings

* chore: another try at python import errors

Looks like the problem is that dbus_mock.py is running as
a script but living in the `lib/` directory where it's part of a
module. Moving it up into the `script/` directory seems to
solve the issue.

script/spec-runner.js

@@ -1,3 +1,5 @@
+#!/usr/bin/env node
+
 const cp = require('child_process')
 const crypto = require('crypto')
 const fs = require('fs')
@@ -39,7 +41,7 @@ getSpecHash().then(([currentSpecHash, currentSpecInstallHash]) => {
   let exe = path.resolve(BASE, utils.getElectronExec())
   const args = process.argv.slice(2)
   if (process.platform === 'linux') {
-    args.unshift(path.resolve(__dirname, 'lib/dbus_mock.py'), exe)
+    args.unshift(path.resolve(__dirname, 'dbus_mock.py'), exe)
     exe = 'python'
   }
   const child = cp.spawn(exe, args, {