Update GitHub builds for flint ball arithmetic

Install libflint-arb-dev in Ubuntu (FLINT 3 not available until 24.04)
and add flint header directory to CPPFLAGS for macOS builds.  Also
install singular from brew instead of factory to get latest version.

.github/workflows/test_build.yml

@@ -72,6 +72,8 @@ jobs:
           brew tap macaulay2/tap
           brew install automake boost tbb ccache ctags llvm make ninja yasm libffi
           brew install --only-dependencies macaulay2/tap/M2
+          HOMEBREW_NO_AUTOREMOVE=1 brew uninstall factory
+          brew install singular
 
 # ----------------------
 #   Install missing tools and libraries for Linux
@@ -85,7 +87,7 @@ jobs:
           sudo apt-get install -y -q --no-install-recommends libboost-stacktrace-dev \
                   libncurses-dev libncurses5-dev libreadline-dev libeigen3-dev liblapack-dev libxml2-dev \
                   libgc-dev libgdbm-dev libglpk-dev libgmp3-dev libgtest-dev libmpfr-dev libmpfi-dev libntl-dev gfan \
-                  libgivaro-dev libboost-regex-dev fflas-ffpack libflint-dev libmps-dev libfrobby-dev \
+                  libgivaro-dev libboost-regex-dev fflas-ffpack libflint-dev libflint-arb-dev libmps-dev libfrobby-dev \
                   libsingular-dev singular-data libcdd-dev cohomcalg topcom 4ti2 libnormaliz-dev normaliz coinor-csdp \
                   libnauty2-dev nauty lrslib polymake phcpack w3c-markup-validator libtbb-dev qepcad libomp-15-dev
 
@@ -160,7 +162,9 @@ jobs:
           make -C ../.. all
           export PYVERSION=`python3 -c "from sys import version_info; \
             print(f'{version_info.major}.{version_info.minor}')"`
-          export CPPFLAGS="-I`brew --prefix`/include -I`brew --prefix libomp`/include"
+          export CPPFLAGS="-I`brew --prefix`/include \
+            -I`brew --prefix libomp`/include         \
+            -I`brew --prefix flint`/include"
           export  LDFLAGS="-L`brew --prefix`/lib -L`brew --prefix libomp`/lib \
             -L/Library/Frameworks/Python.framework/Versions/${PYVERSION}/lib"
           ../../configure --enable-download --with-python --with-system-gc