TestGLDrawing.test_text fails on OSX while processing font

`kiva.tests.test_gl_drawing.TestGLDrawing.test_text` fails on OSX with the following error:
```
======================================================================
ERROR: test_text (kiva.tests.test_gl_drawing.TestGLDrawing)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/Users/runner/work/enable/enable/.edm/envs/enable-test-3.6-pyqt5/lib/python3.6/site-packages/kiva/tests/drawing_tester.py", line 72, in test_text
self.gc.show_text("hello kiva")
File "/Users/runner/work/enable/enable/.edm/envs/enable-test-3.6-pyqt5/lib/python3.6/site-packages/kiva/gl.py", line 339, in show_text
return self.show_text_at_point(text, *point)
File "/Users/runner/work/enable/enable/.edm/envs/enable-test-3.6-pyqt5/lib/python3.6/site-packages/kiva/gl.py", line 345, in show_text_at_point
pyglet_font = GetFont(self._current_font)
File "/Users/runner/work/enable/enable/.edm/envs/enable-test-3.6-pyqt5/lib/python3.6/site-packages/kiva/gl.py", line 273, in GetFont
pyglet_font = load_font(font.findfontname(), font.size, bold,
File "/Users/runner/work/enable/enable/.edm/envs/enable-test-3.6-pyqt5/lib/python3.6/site-packages/kiva/fonttools/font.py", line 105, in findfontname
return fp.get_name()
File "/Users/runner/work/enable/enable/.edm/envs/enable-test-3.6-pyqt5/lib/python3.6/site-packages/kiva/fonttools/font_manager.py", line 860, in get_name
prop_dict = getPropDict(TTFont(str(font)))
File "/Users/runner/work/enable/enable/.edm/envs/enable-test-3.6-pyqt5/lib/python3.6/site-packages/fontTools/ttLib/ttFont.py", line 140, in __init__
self.reader = SFNTReader(file, checkChecksums, fontNumber=fontNumber)
File "/Users/runner/work/enable/enable/.edm/envs/enable-test-3.6-pyqt5/lib/python3.6/site-packages/fontTools/ttLib/sfnt.py", line 59, in __init__
raise TTLibError("specify a font number between 0 and %d (inclusive)" % (numFonts - 1))
fontTools.ttLib.TTLibError: specify a font number between 0 and 3 (inclusive)
```

(See log file: [enable-osx-test-failure.txt](https://github.com/enthought/enable/files/5808812/enable-osx-test-failure.txt), extracted from https://github.com/enthought/enable/pull/540)

Since enable CI has not run against OSX until recently, and the test case has been unintentionally skipped on OSX while intended to be skipped on Windows, and is further skipped if pyglet is not installed (which wasn't installed in the default environment from edmtool.py), it is hard to tell when the regression occurs if this is a regression or if it has been failing from the beginning when the test was added.