Python error on pip upgrade step in builds

[bskinn]

Details

• Read the Docs project URL: sphobjinv.readthedocs.io
• Build URL (if applicable): https://readthedocs.org/projects/sphobjinv/builds/10328312/
• Read the Docs username (if applicable): bskinn

Expected Result

A build that completed fine before should complete fine again.

Actual Result

The build fails at the pip upgrade step due to an ImportError.

A recent build worked fine, and then one didn't, and then it worked fine again. Now, though, it seems to be consistently failing.

[bskinn]

Ah, whoops -- looks like this is the same as #6566, or closely related.

[bskinn]

Wiping the build environment seems to have worked for these failures. 👍