REV: restore pyparsing to latest version for doc builds

[rrjbca]

Description

Reverts #500. To be merged after a new matplotlib release fixing the incompatibility with pyparsing 3.x

Checklist

• [x] Follow the Contributor Guidelines
• [ ] Write unit tests
• [ ] Write documentation strings
• [x] Assign someone from your working team to review this pull request
• [x] Assign someone from the infrastructure team to review this pull request

[rrjbca]

Docs build successfully with pyparsing 3.0.2 and matplotlib [3.4.3, v3.5.x]