Fix ruby-docs being incomplete

common.mk says

install-capi: capi pre-install-capi do-install-capi post-install-capi
…
install-doc: rdoc pre-install-doc do-install-doc post-install-doc

instead of

install-capi: capi $(DOT_WAIT) pre-install-capi $(DOT_WAIT) do-install-capi $(DOT_WAIT) post-install-capi
…
install-doc: rdoc $(DOT_WAIT) pre-install-doc $(DOT_WAIT) do-install-doc $(DOT_WAIT) post-install-doc

This means that Make may run doxygen and rdoc --ri concurrently with running rbinstall.rb copying their outputs to $pkgdir. Meaning that the outputs might be incomplete. Indeed, we see this with extra/ruby-docs-3.2.5-1; the /usr/share/doc/ruby/capi/html/ directory is empty except for doxygen_crawl.html.

Fix this by having rdoc and capi have already been made during build().

I did this as a separate make invocation (add make rdoc capi instead of changing the existing invocation to make all rdoc capi because if this mistake exists, it made me nervous that a similar mistake exists with rdoc or capi not properly depending on generated ruby or c sources.