Backport #23281
This branch continues the work of #23092 and attempts to rid the
codebase of any `nil` contexts when using a `RenderContext`.
Anything that renders markdown or does post processing may call
`markup.sha1CurrentPatternProcessor()`, and this runs
`git.OpenRepository()`, which needs a context. It will panic if the
context is `nil`. This branch attempts to _always_ include a context
when creating a `RenderContext` to prevent future crashes.
Co-authored-by: Jonathan Tran <jon@allspice.io>
dcf1717793