Merge branch 'ab/detox-gettext-tests'

Get rid of "GETTEXT_POISON" support altogether, which may or may
not be controversial.

* ab/detox-gettext-tests:
  tests: remove uses of GIT_TEST_GETTEXT_POISON=false
  tests: remove support for GIT_TEST_GETTEXT_POISON
  ci: remove GETTEXT_POISON jobs

diff --cc .github/workflows/main.yml
Simple merge

diff --cc ci/install-dependencies.sh
Simple merge

diff --cc config.c
Simple merge

diff --cc gettext.c
Simple merge

diff --cc t/README
Simple merge

diff --cc t/t1305-config-include.sh
Simple merge

diff --cc t/t3406-rebase-message.sh
Simple merge

diff --cc t/t7201-co.sh
Simple merge

diff --cc t/t9902-completion.sh
Simple merge

diff --cc t/test-lib-functions.sh
Simple merge

diff --cc t/test-lib.sh
Simple merge