don't always call load_all_plugins

devscripts/run_tests.py

@@ -51,7 +51,7 @@ def run_tests(*tests, pattern=None, ci=False, load_plugins=False):
     try:
         return subprocess.call(arguments, env={
             **os.environ,
-            '_YT_DLP_TEST_DO_LOAD_PLUGINS': '1' if load_plugins else '',
+            'YTDLP_NO_PLUGINS': '1' if os.environ.get('YTDLP_NO_PLUGINS') or not load_plugins else '',
         })
     except FileNotFoundError:
         pass

test/helper.py

@@ -88,7 +88,7 @@ class FakeYDL(YoutubeDL):
 
 
 def gettestcases(include_onlymatching=False):
-    if os.environ.get('_YT_DLP_TEST_DO_LOAD_PLUGINS'):
+    if not os.environ.get('YTDLP_NO_PLUGINS'):
         import yt_dlp.plugins as plugins
         plugins.load_all_plugins()
     for ie in yt_dlp.extractor.gen_extractors():