feat: defaults puppeteer and playwright to new headless mode (garris/BackstopJS/garris#1525)

Author: dgrebb

core/util/runPlaywright.js

@@ -36,7 +36,7 @@ module.exports.createPlaywrightBrowser = async function (config) {
   const playwrightArgs = Object.assign(
     {},
     {
-      headless: config.debugWindow ? false : config?.engineOptions?.headless || true
+      headless: config.debugWindow ? false : config?.engineOptions?.headless || 'new'
     },
     config.engineOptions
   );

core/util/runPuppet.js

@@ -71,7 +71,7 @@ async function processScenarioView (scenario, variantOrScenarioLabelSafe, scenar
     {},
     {
       ignoreHTTPSErrors: true,
-      headless: config.debugWindow ? false : config?.engineOptions?.headless || true
+      headless: config.debugWindow ? false : config?.engineOptions?.headless || 'new'
     },
     config.engineOptions
   );