fix: Update max_instances default to reflect actual value (#2302)

The default maximum instances for cloud functions is 100, not 0. Updated
the `expected_max_instances` in the `parametrize` decorator to 100 for
the 'no-set' and 'set-None' test cases to accurately reflect the runtime
behavior.

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Fixes b/465212379 🦕

Author: jialuoo

tests/system/large/functions/test_remote_function.py

@@ -1651,13 +1651,12 @@ def square(x):
             return x * x
 
 
-# Note: Zero represents default, which is 100 instances actually, which is why the remote function still works
-# in the df.apply() call here
+# The default value of 100 is used if the maximum instances value is not set.
 @pytest.mark.parametrize(
     ("max_instances_args", "expected_max_instances"),
     [
-        pytest.param({}, 0, id="no-set"),
-        pytest.param({"cloud_function_max_instances": None}, 0, id="set-None"),
+        pytest.param({}, 100, id="no-set"),
+        pytest.param({"cloud_function_max_instances": None}, 100, id="set-None"),
         pytest.param({"cloud_function_max_instances": 1000}, 1000, id="set-explicit"),
     ],
 )