ci: explicitly install pygments and certifi on macos

ci: explicitly install pygments and certifi on macos

The documentation build on macOS started failing because of errors with
the pygments and certifi modules. Homebrew is not automatically
installing pygments and python-certifi which are listed as packages that
sphinx-doc depends on because they are already present in the runner
image at the required versions (2.16.1 and 2023.7.22, respectively).
Explicitly installing the two packages bumps the versions to slightly
newer ones (2.16.1_1 and 2023.7.22_1, respectively). This appears to
resolve the documentation build problem.

https://formulae.brew.sh/formula/sphinx-doc
https://github.com/axboe/fio/actions/runs/6533001329/job/17739452911#step:13:155
https://github.com/vincentkfu/fio/actions/runs/6535039949/job/17743571376#step:13:148
https://github.com/vincentkfu/fio/actions/runs/6535229986/job/17744177918#step:6:10

Signed-off-by: Vincent Fu <vincent.fu@samsung.com>