Use brew's readline in macOS autotools GitHub builds

It's keg-only to avoid conflicting with libedit provided by the
system, so we need to specify the paths in order for it to be
detected.  Otherwise, we end up building it every time!

.github/workflows/test_build.yml

@@ -157,8 +157,12 @@ jobs:
           ../../autogen.sh
           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  LDFLAGS="-L`brew --prefix`/lib -L`brew --prefix libomp`/lib \
+          export CPPFLAGS="-I`brew --prefix`/include \
+            -I`brew --prefix libomp`/include         \
+            -I`brew --prefix readline`/include"
+          export  LDFLAGS="-L`brew --prefix`/lib \
+            -L`brew --prefix libomp`/lib         \
+            -L`brew --prefix readline`/lib       \
             -L/Library/Frameworks/Python.framework/Versions/${PYVERSION}/lib"
           export F77=gfortran-14
           ../../configure --enable-download --with-system-gc