Meson-build: Linker-error in hb-paint-tests for disabled freetype and cairo

[Emanuesson]

I came across this problems, as I wanted to compile a project that depends on
harfbuzz with the meson-build-flag -Dwrap_mode=forcefallback. However,
the problem can also be reproduced on harfbuzz itself:

• Check out a recent state of harfbuzz (e.g. 6.0.0-978-gcb47dca74)
• Configure a build-directory with meson-build:
  meson setup build -Dwrap_mode=forcefallback -Dfreetype=disabled -Dcairo=disabled
• Try to compile and test it with:
  meson compile -C build && meson test -C build

Expected:
All build-targets and tests are build and can be executed successfully

Observed:
Linker complains about a missing reference:
harfbuzz/build/../test/api/test-paint.c:520: undefined reference to 'have_ft_colrv1'

Proposed change:
IMHO the test can easily be made compatible, for the else-case of #ifdef HB_HAS_FREETYPE.
The function have_ft_colrv1 may then just always return FALSE.