FIX: Test dummy credentials to avoid ADO secret scanner false positive (#504)

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[AB#43894](https://sqlclientdrivers.visualstudio.com/c6d89619-62de-46a0-8b46-70b92a84d85e/_workitems/edit/43894)

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### Summary   
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This pull request updates test credentials in the
`tests/test_020_bulkcopy_auth_cleanup.py` file to use more generic and
less sensitive values for the database connection and password
assertions.

Test credential updates:

* Changed the database connection string in the `_make_cursor` call to
use `Server=localhost` and `PWD=mypwd` instead of
`Server=tcp:test.database.windows.net` and `PWD=password123` to avoid
using production-like or sensitive values in tests.
* Updated the corresponding password assertion in the `capture_context`
test to match the new password value (`mypwd`).

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Co-authored-by: gargsaumya <saumyagarg.100@gmail.com>

Author: bewithgaurav

tests/test_020_bulkcopy_auth_cleanup.py

@@ -80,7 +80,7 @@ def test_no_auth_type_leaves_fields_intact(self, mock_logger):
         mock_logger.is_debug_enabled = False
 
         cursor = _make_cursor(
-            "Server=tcp:test.database.windows.net;Database=testdb;" "UID=sa;PWD=password123",
+            "Server=localhost;Database=testdb;" "UID=sa;PWD=mypwd",
             None,  # no AD auth
         )
 
@@ -107,4 +107,4 @@ def capture_context(ctx, **kwargs):
 
         assert "access_token" not in captured_context
         assert captured_context.get("user_name") == "sa"
-        assert captured_context.get("password") == "password123"
+        assert captured_context.get("password") == "mypwd"