invert wrong logic, skip cfitsio on macOS

common_utils.sh

@@ -432,10 +432,10 @@ function install_pypy {
     "ppc64le") suffix="ppc64le";;
     "s30x")    suffix="s390x";;
     "aarch64")  suffix="aarch64";;
-    *) if [ -z "$IS_OSX" ]; then
-            suffix = "osx64";
+    *) if [ -n "$IS_OSX" ]; then
+            suffix="osx64";
        else
-            echo unknown platform $PLAT; exit 1
+            echo unknown platform "$PLAT"; exit 1
        fi;;
     esac
 

tests/test_library_builders.sh

@@ -50,7 +50,10 @@ if [ -z "$IS_OSX" ]; then
     suppress build_lzo
 fi
 suppress build_ragel
-suppress build_cfitsio
+if [ -z "$IS_OSX" ]; then
+    # already installed in the macOS image, so `brew install cfitsio` fails
+    suppress build_cfitsio
+fi
 suppress build_new_zlib
 suppress build_hdf5