Fixes #3239

See https://github.com/Vampire/setup-wsl/issues/50 / https://github.com/actions/runner-images/discussions/8791

This should only annoy those testing their PRs; real users should never set this env var

This should be improved in the future, but is fine for now

 - disable failing Alpine tests
 - disable Ubuntu-18.04 tests on node 18+
 - add Ubuntu-20.04 tests

avoids `expr: warning: ^lts/-[1-9][0-9]*: using ^ as the first character of a basic regular expression is not portable; it is ignored`

Fixes https://github.com/openjs-foundation/security-collab-space/issues/35.

Signed-off-by: zhangdiandian <1635468471@qq.com>

Path lists in environmental variables often give special meaning to
empty entries (e.g. in PATH or MANPATH). These are represented by
leading or trailing colons, or by doubled colons in the middle of the
list.

Adjust the awk invocation to correctly deal with trailing colons by
printing the separator before every field except the first, and then
printing the final separator that is read from the input - this will
either be a colon or the null string. This preserves leading and
trailing colons in all cases while not adding extra colons in the wrong
place.

Add test to confirm the correct behaviour.

Fixes #3144

Co-authored-by: heungjun.park <rockheung@gmail.com>
Co-authored-by: Jordan Harband <ljharb@gmail.com>

See https://unix.stackexchange.com/a/555061/137489

See https://github.com/npm/cli/pull/6674

Signed-off-by: emmanuel-ferdman <35470921+emmanuel-ferdman@users.noreply.github.com>

I had to dig into #2410 to learn about the `PROFILE=/dev/null` technique to install without appending to my shell config. Figured this note would be good to add in the main installation docs.
Also added a note on how to do this as a one-liner which was not obvious for me.

Fixes #3104