[jat255]

This PR adds a shared composite action that installs the R system requirements on Linux without Chromium. The R jobs no longer depend on the xtradeb Launchpad PPA that pak adds for Chromium. This PPA has caused at least two outages that I've noticed while working, which is kind of a drag.

Details (agent-written)

Chromium is the only one of the 26 system requirements that comes from outside Ubuntu's archive, and pak adds ppa:xtradeb/apps for it. The five R CMD check jobs on Ubuntu installed it too, although they set COMMONS_SKIP_BROWSER_TESTS and never start a browser.

r-sysreqs asks pak for the requirements that setup-r-dependencies would install for the same extra-packages and needs, drops the chrome requirement, and installs the rest. Each R workflow runs it first, then runs setup-r-dependencies with PKG_SYSREQS=false. The citation browser job uses the Chrome that ships in the runner image, and its existing Locate Chrome step fails if chromote cannot find it. macOS and Windows do not change, because pak installs no system packages there.

Rejected alternatives: retrying setup-r-dependencies (the last outage lasted about 40 minutes), and turning system requirements off entirely (the runner image does not promise cmake, protobuf, libnode, or unixodbc-dev).

Testing: the action's script ran in an Ubuntu 24.04 container against Package Manager's latest, and actionlint passes on the three workflows. In this PR's checks, every Ubuntu R CMD check job and pkgdown pass without adding the PPA, and the citation browser tests (30) pass on the runner's Chrome.

setup-r-dependencies still prints "Missing 26 system packages" in its log. With PKG_SYSREQS=false, pak lists every requirement without checking what is installed, so the message is expected.

[simonpcouch]

It seems like the underlying issue may have been resolved upstream yesterday—this commit now guards every Ubuntu pre-install command with [ $(which google-chrome) ] || …, for 22.04/24.04/26.04. Our Actions runs yesterday hadn't picked up this commit yet, but they should now—could we wait on this and see if the issue has now resolved itself? I'd prefer to continue to get upstream improvements from pak and its toolchain for free.

[jat255]

It seems like the underlying issue may have been resolved upstream yesterday—this commit now guards every Ubuntu pre-install command with [ $(which google-chrome) ] || …, for 22.04/24.04/26.04. Our Actions runs yesterday hadn't picked up this commit yet, but they should now—could we wait on this and see if the issue has now resolved itself? I'd prefer to continue to get upstream improvements from pak and its toolchain for free.

Ha, in my rage to workaround this, I didn't think to look at where xtradeb was coming from. Thanks @schloerke! I think that fix will work and agree with you better not to have the workaround here.