Include LTO checks in GHA

[krlmlr]

r-hub/containers#57, and making the check fail fatally in case of LTO errors.

Ways to trigger errors: 35fa3f2

[krlmlr]

First step: reproduce LTO failures with igraph 2.0.0 release candidates, and no LTO failures with current mainline. We'll think about automation as a next step.

[krlmlr]

Need to find a simple way to trigger LTO checks.

New project, useful here: https://github.com/r-hub/rhub2

[krlmlr]

Docs: https://cran.r-project.org/doc/manuals/r-release/R-exts.html#Using-Link_002dtime-Optimization

Check with R CMD INSTALL --use-LTO .

[krlmlr]

Use gcc13 container from rhub2 with --use-LTO .