Rename the test-lin-san GitLab CI job

[aitap]

As it turns out, #6476 broke GitLab CI because test stage names are expected to follow a pattern of test-<platform>-<R version>[-<suffixes...>]:

data.table/.ci/publish.R

Lines 162 to 168 in 3afc750

	if (length(tmp) < 3L) stop("test job names must be test-[lin|win|mac]-[r.version]-...")
	v = tmp[3L]
	if (identical(v, "rel")) "r-release"
	else if (identical(v, "dev")) "r-devel"
	else if (identical(v, "old") || identical(v, "ancient")) "r-oldrel"
	else {
	if (grepl("\\D", v)) stop("third word in test job name must be rel/dev/old or numbers of R version")

(And if <R version> is not rel, dev, or old, it must be a series of digits to be joined by dots.)

Perhaps this needs a comment in .gitlab-ci.yml, but I'm not sure where to place it.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.59%. Comparing base (3afc750) to head (81f5452).
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6866   +/-   ##
=======================================
  Coverage   98.59%   98.59%           
=======================================
  Files          79       79           
  Lines       14660    14660           
=======================================
  Hits        14454    14454           
  Misses        206      206           

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[MichaelChirico]

linking the specific failed log (I was a little confused to see the test-lin-san job had passed):

https://gitlab.com/Rdatatable/data.table/-/jobs/9409409168

[jangorecki]

https://github.com/Rdatatable/data.table/blob/master/.ci/README.md
This may be best place to mention such pattern, and possibly mention the reason for that as well.