build: more flexible python-pptx deps

[RobPasMue]

Closes #293

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.14%. Comparing base (fbc3b59) to head (e69f57a).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #297   +/-   ##
=======================================
  Coverage   80.14%   80.14%           
=======================================
  Files          25       25           
  Lines        7061     7061           
  Branches     1330     1330           
=======================================
  Hits         5659     5659           
  Misses        983      983           
  Partials      419      419           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[viseshrp]

Hi. Thanks for the PR. Unfortunately, this has to be strictly 0.6.19 due to an issue. @RobPasMue