update firefox-ubuntu to 20.04

Author: catsout

node/flatpak_node_generator/providers/special.py

@@ -344,7 +344,7 @@ async def _handle_playwright(self, package: Package) -> None:
                 if revision < 1140:
                     dl_file = 'firefox-linux.zip'
                 else:
-                    dl_file = 'firefox-ubuntu-18.04.zip'
+                    dl_file = 'firefox-ubuntu-20.04.zip'
             elif name == 'webkit':
                 url_tp = 'https://playwright.azureedge.net/builds/webkit/%d/%s'
                 if revision < 1317: