build: add gettext-tools dependency from MSYS2 repo.

gettext was recently split into 2 packages. While we didn't have the issue on
hmartinez82's runner, because old packages are not wiped out (as they should),
this issue first appeared on our new Arm runners.

This fixes the following error in our Windows build:

> /usr/bin/msgfmt: cannot locate ITS rules for ../data/tips/gimp-tips.xml.in

See:
* https://gitlab.gnome.org/Infrastructure/gimp-web-devel/-/merge_requests/52
* msys2/MINGW-packages#19913

build/windows/gitlab-ci/all-deps-uni.txt

@@ -8,6 +8,7 @@ DEPS_ARCH_brotli
 DEPS_ARCH_cairo
 DEPS_ARCH_cfitsio
 DEPS_ARCH_drmingw
+DEPS_ARCH_gettext-tools
 DEPS_ARCH_gexiv2
 DEPS_ARCH_ghostscript
 DEPS_ARCH_gi-docgen
@@ -46,4 +47,4 @@ DEPS_ARCH_python-gobject
 DEPS_ARCH_shared-mime-info
 DEPS_ARCH_suitesparse
 DEPS_ARCH_vala
-DEPS_ARCH_xpm-nox
+DEPS_ARCH_xpm-nox