tests: fix Python 3.8/3.9 deprecation warnings in pytest.ini

Updated the new regexes for `google-auth` warnings to handle leading whitespace/newlines (`.*You are using a Python version 3.X`).
Preserved the original regexes for `google-api-core` warnings (`You are using a non-supported Python version (3.X...`) to ensure all warning variants are suppressed.

Fixes #374

Author: google-labs-jules[bot]

pytest.ini

@@ -14,10 +14,10 @@ filterwarnings =
     # Remove after support for Python 3.8 is dropped
     ignore:You are using a non-supported Python version \(3\.8:DeprecationWarning
     ignore:You are using a non-supported Python version \(3\.8:FutureWarning
-    ignore:You are using a Python version 3\.8:FutureWarning
+    ignore:.*You are using a Python version 3\.8:FutureWarning
     # Remove after support for Python 3.9 is dropped:
     ignore:You are using a Python version \(3\.9:FutureWarning
-    ignore:You are using a Python version 3\.9:FutureWarning
+    ignore:.*You are using a Python version 3\.9:FutureWarning
     ignore:You are using a non-supported Python version \(3\.9:DeprecationWarning
     ignore:You are using a non-supported Python version \(3\.9:FutureWarning
     # Remove after support for Python 3.10 is dropped