Do not mutate kwargs["binary_args"] (#37308)

Fixup of #37255, we should not modify existing `kwargs["binary_args"]`
or else subsuite's `binary_args` will apply in non subsuite runs.

Testing: I verified fix in my personal fork run with vello (where I
actually use subsuite).

Signed-off-by: sagudev <16504129+sagudev@users.noreply.github.com>

tests/wpt/meta/MANIFEST.json

@@ -516386,11 +516386,11 @@
         ]
        },
        "servo.py": [
-        "49a2613ff12ba4f3b085549a31266a21861bbaf1",
+        "07441780ccc7682c6b7616271aeb9a40310a433a",
         []
        ],
        "servodriver.py": [
-        "a8aa5ae001b1ecd53a7f2f4515efa299c9ce8809",
+        "f72f2257a3817e33817dc7a190da8e61cf6442da",
         []
        ],
        "webkit.py": [

tests/wpt/tests/tools/wptrunner/wptrunner/browsers/servo.py

@@ -38,11 +38,10 @@ def check_args(**kwargs):
 
 
 def browser_kwargs(logger, test_type, run_info_data, config, subsuite, **kwargs):
-    kwargs["binary_args"].extend(subsuite.config.get("binary_args", []))
     return {
         "binary": kwargs["binary"],
         "debug_info": kwargs["debug_info"],
-        "binary_args": kwargs["binary_args"],
+        "binary_args": kwargs["binary_args"] + subsuite.config.get("binary_args", []),
         "user_stylesheets": kwargs.get("user_stylesheets"),
         "ca_certificate_path": config.ssl_config["ca_cert_path"],
     }

tests/wpt/tests/tools/wptrunner/wptrunner/browsers/servodriver.py

@@ -40,10 +40,9 @@ def check_args(**kwargs):
 
 
 def browser_kwargs(logger, test_type, run_info_data, config, subsuite, **kwargs):
-    kwargs["binary_args"].extend(subsuite.config.get("binary_args", []))
     return {
         "binary": kwargs["binary"],
-        "binary_args": kwargs["binary_args"],
+        "binary_args": kwargs["binary_args"] + subsuite.config.get("binary_args", []),
         "debug_info": kwargs["debug_info"],
         "server_config": config,
         "user_stylesheets": kwargs.get("user_stylesheets"),