build: install MSYS2 autotools package.

Some tools have been moved. `aclocal` (and likely other tools, but this
was the first one making an error in the deps-win*-native CI jobs) is
now in `automake-wrapper` package, which itself is a dependency of
`autotools`.

Cf. msys2/MINGW-packages#11114

build/windows/gitlab-ci/build-deps-msys2.sh

@@ -25,6 +25,7 @@ pacman --noconfirm -Suy
 pacman --noconfirm -S --needed \
     base-devel \
     mingw-w64-$MSYS2_ARCH-toolchain \
+    mingw-w64-$MSYS2_ARCH-autotools \
     mingw-w64-$MSYS2_ARCH-meson \
     \
     mingw-w64-$MSYS2_ARCH-cairo \

build/windows/gitlab-ci/build-gimp-msys2.sh

@@ -24,6 +24,7 @@ pacman --noconfirm -Suy
 pacman --noconfirm -S --needed \
     base-devel \
     mingw-w64-$MSYS2_ARCH-toolchain \
+    mingw-w64-$MSYS2_ARCH-autotools \
     mingw-w64-$MSYS2_ARCH-ccache \
     \
     mingw-w64-$MSYS2_ARCH-appstream-glib \