Tests: ignore a branch for coverage check

lib/libvips.js

@@ -94,7 +94,7 @@ const pkgConfigPath = function () {
     const brewPkgConfigPath = spawnSync(
       'which brew >/dev/null 2>&1 && brew environment --plain | grep PKG_CONFIG_LIBDIR | cut -d" " -f2',
       spawnSyncOptions
-    ).stdout || '';
+    ).stdout /* istanbul ignore next */ || '';
     return [
       brewPkgConfigPath.trim(),
       env.PKG_CONFIG_PATH,