[tox/pytest] Fix some warnings in tests

[ctrlcctrlv]

Fixes three warnings—

Tests/ttLib/tables/_g_l_y_f_test.py::GlyfTableTest::test_getPhantomPoints
  /home/fred/Workspace/fonttools/Tests/ttLib/tables/_g_l_y_f_test.py:379: DeprecationWarning: 'getPhantomPoints' is deprecated; use '_getPhantomPoints' instead
    font["glyf"].getPhantomPoints(".notdef", font, 0),

Tests/varLib/instancer/names_test.py:218
  /home/fred/Workspace/fonttools/Tests/varLib/instancer/names_test.py:218: DeprecationWarning: invalid escape sequence \[
    with pytest.raises(ValueError, match="Cannot find Axis Values \['wght=200'\]"):

Tests/varLib/instancer/instancer_test.py: 12 warnings
  /home/fred/Workspace/fonttools/Tests/varLib/instancer/instancer_test.py:53: DeprecationWarning: 'getCoordinatesAndControls' is deprecated; use '_getCoordinatesAndControls' instead
    return list(varfont["glyf"].getCoordinatesAndControls(glyphname, varfont)[0])