Update badges and remove pdf gen from rtd

[brynpickering]

Fixes badges (I tried sneakily force pushing a minor change, but realised there's more to it)

Summary of changes in this pull request:

• Update badges to work with current CI / apps
• Update badges to all rounded since some can't do flat-square styling
• Remove PDF generation of docs since the PDF build has been failing horribly for ~5 months (e.g. here)

Reviewer checklist:

• [ ] Test(s) added to cover contribution
• [ ] Documentation updated
• [ ] Changelog updated
• [ ] Coverage maintained or improved

[codecov[bot]]

Codecov Report

Merging #503 (b65b419) into main (eb75c2a) will increase coverage by 0.16%. Report is 4 commits behind head on main. The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #503      +/-   ##
==========================================
+ Coverage   92.20%   92.36%   +0.16%     
==========================================
  Files          32       32              
  Lines        4016     4089      +73     
  Branches      957      964       +7     
==========================================
+ Hits         3703     3777      +74     
+ Misses        198      197       -1     
  Partials      115      115              

see 15 files with indirect coverage changes