make_osx: disable set -e during test of signing identity

contrib/osx/make_osx

@@ -32,8 +32,10 @@ which xcodebuild > /dev/null 2>&1 || fail "Please install xcode command line too
 if [ -n "$CODESIGN_CERT" ]; then
     # Test the identity is valid for signing by doing this hack. There is no other way to do this.
     cp -f /bin/ls ./CODESIGN_TEST
+    set +e
     codesign -s "$CODESIGN_CERT" --dryrun -f ./CODESIGN_TEST > /dev/null 2>&1
     res=$?
+    set -e
     rm -f ./CODESIGN_TEST
     if ((res)); then
         fail "Code signing identity \"$CODESIGN_CERT\" appears to be invalid."