update_3rdparty: move dict related imports into method

I'm trying to update pdf.js in the bleeding edge CI jobs. It complains
that either it can't find PyQt or it can't find yaml depending on how I
invoke tox. Joy. Since dict stuff isn't run by default in this script
hopefully that is the only broken import path and moving it into the
function lets the pdfjs (and ace) bit of the script work fine.

Actually, looking at the stack traces below, both of them are from dict
related code!

    tox exec -re bleeding -- python scripts/dev/update_3rdparty.py --gh-token ***
      Traceback (most recent call last):
        File "/__w/qutebrowser/qutebrowser/scripts/dev/update_3rdparty.py", line 20, in <module>
          from scripts import dictcli
        File "/__w/qutebrowser/qutebrowser/scripts/dev/../../scripts/dictcli.py", line 25, in <module>
          from qutebrowser.browser.webengine import spell
        File "/__w/qutebrowser/qutebrowser/scripts/dev/../../scripts/../qutebrowser/browser/webengine/spell.py", line 14, in <module>
          from qutebrowser.utils import log, message, standarddir
        File "/__w/qutebrowser/qutebrowser/scripts/dev/../../scripts/../qutebrowser/utils/message.py", line 15, in <module>
          from qutebrowser.qt.core import pyqtSignal, pyqtBoundSignal, QObject
        File "/__w/qutebrowser/qutebrowser/scripts/dev/../../scripts/../qutebrowser/qt/core.py", line 17, in <module>
          machinery.init_implicit()
        File "/__w/qutebrowser/qutebrowser/scripts/dev/../../scripts/../qutebrowser/qt/machinery.py", line 278, in init_implicit
          raise NoWrapperAvailableError(info)
      qutebrowser.qt.machinery.NoWrapperAvailableError: No Qt wrapper was importable.

    python scripts/dev/update_3rdparty.py --gh-token ***
      Traceback (most recent call last):
        File "/__w/qutebrowser/qutebrowser/scripts/dev/update_3rdparty.py", line 20, in <module>
          from scripts import dictcli
        File "/__w/qutebrowser/qutebrowser/scripts/dev/../../scripts/dictcli.py", line 25, in <module>
          from qutebrowser.browser.webengine import spell
        File "/__w/qutebrowser/qutebrowser/scripts/dev/../../scripts/../qutebrowser/browser/webengine/spell.py", line 14, in <module>
          from qutebrowser.utils import log, message, standarddir
        File "/__w/qutebrowser/qutebrowser/scripts/dev/../../scripts/../qutebrowser/utils/message.py", line 17, in <module>
          from qutebrowser.utils import usertypes, log
        File "/__w/qutebrowser/qutebrowser/scripts/dev/../../scripts/../qutebrowser/utils/usertypes.py", line 16, in <module>
          from qutebrowser.utils import log, qtutils, utils
        File "/__w/qutebrowser/qutebrowser/scripts/dev/../../scripts/../qutebrowser/utils/qtutils.py", line 39, in <module>
          from qutebrowser.utils import usertypes, utils
        File "/__w/qutebrowser/qutebrowser/scripts/dev/../../scripts/../qutebrowser/utils/utils.py", line 29, in <module>
          import yaml
      ModuleNotFoundError: No module named 'yaml'

scripts/dev/update_3rdparty.py

@@ -17,8 +17,6 @@ import sys
 
 sys.path.insert(
     0, os.path.join(os.path.dirname(__file__), os.pardir, os.pardir))
-from scripts import dictcli
-from qutebrowser.config import configdata
 
 
 def download_nsis_plugins():
@@ -160,6 +158,8 @@ def update_ace():
 
 def test_dicts():
     """Test available dictionaries."""
+    from scripts import dictcli
+    from qutebrowser.config import configdata
     configdata.init()
     for lang in dictcli.available_languages():
         print('Testing dictionary {}... '.format(lang.code), end='')