Build: Dev: Install the necessary "column" dependency for "make [help]"

act's catthehacker/ubuntu:runner-24.04 image doesn't have the bsdmainutils package installed.

Compatibility: "read -N 1" is only available in Bash 4.1+

Mac OS still ships with Bash 3.2 :-( Fall back to the original prompting that requires conclusion via Enter then.
Note: Even though the tests use "printf y", this still gets accepted, as there'll be EOF after that. In real use (when stdin from the terminal stays open), a concluding Enter is mandatory, though.

TESTSFIX: User add-ons that override built-in actions may break tests

If TODO_ACTIONS_DIR is already defined, the defaulting in todo.sh are skipped. The user may have custom add-ons that override built-in actions; any incompatible behavior would negatively affect the tests then.
By setting the variable to the first default location, we avoid this interference.

Documentation: Mention ~/.todo/config as just one of the defaults

As there are several others, now shown in the help for -d.
I don't want to duplicate the entire list here as there's a high risk of those lists diverging.

Fixes todotxt#342

Documentation: Correct quoting in todo.sh help list

Though the double quoting doesn't do harm when the single backslash is followed by the | character (\| is no valid escape sequence), it's technically more correct to use single quotes, and also is more in line with the quoting advice given directly below it.

Update changelog. Tag v2.12.0

Merge remote-tracking branch 'upstream/master' into enh-configurable-…

…sigil-patterns

Merge remote-tracking branch 'upstream/master' into enh-completion-files

FIX: Compatibility: sed \+ multi not supported on MacOS

Use the POSIX \{1,\} instead.