Tests in recirq/documentation_utils_test.py are inadequate

[mhucka]

Describe the issue

As discovered in the comments on PR #415, the current test cases in recirq/documentation_utils_test.py did not catch a problem that users experienced in a Colab environment. The tests need to be enhanced to address this limitation.

How can the issue be reproduced?

See this comment by @dstrain115 at PR #415.