Use github actions to build pkgdown site, check package and code coverage

[chacalle]

Originally used this example to create github actions workflow https://github.com/r-lib/actions/tree/master/examples#build-pkgdown-site

Then removed extra steps that aren't in the ggplot2 github actions workflow https://github.com/tidyverse/ggplot2/blob/master/.github/workflows/pkgdown.yaml

[chacalle]

The step that installs the remotes package seems to be returning a warning that github actions is turning into an error.

install.packages("remotes")
Installing package into ‘/Users/runner/runners/2.165.2/work/_temp/Library’
(as ‘lib’ is unspecified)
##[warning]Warning: unable to access index for repository https://cloud.r-project.org/bin/macosx/el-capitan/contrib/3.6:
  cannot open URL 'https://cloud.r-project.org/bin/macosx/el-capitan/contrib/3.6/PACKAGES'
installing the source package ‘remotes’

trying URL 'https://cloud.r-project.org/src/contrib/remotes_2.1.1.tar.gz'
Content type 'application/x-gzip' length 134042 bytes (130 KB)
==================================================
downloaded 130 KB

Looking at the ggplot2 workflow logs this seems to work fine for them https://github.com/tidyverse/ggplot2/runs/509138420?check_suite_focus=true

[chacalle]

I'm seeing the same error as us in dplyr with their recent builds so I think something is messed up with cran or github actions. https://github.com/tidyverse/dplyr/runs/536409117?check_suite_focus=true

I think once that is fixed this will work