fix(testing): enable REPL launch print test for all non-Darwin platforms (#26157)

# PR: Enable REPL launch print test for all non-Darwin platforms

## Related Issue
Fixes #26156 

## Changes Proposed
* **[Test Suite - Shell Integration]**: In
`python_files/tests/test_shell_integration.py`, changed the conditional
guard for `test_print_statement_non_darwin` from `if sys.platform ==
"win32":` to `if sys.platform != "darwin":` so that the REPL launch
print banner is verified on Linux and other non-Darwin Unix environments
in addition to Windows.
* **[Platform Parity]**: Eliminates the test gap where non-Darwin Unix
systems were missing test coverage for the Native REPL launch message.

## How Has This Been Tested?
Please describe the tests that you ran to verify your changes.
* [x] Test A: Pytest run on
`python_files/tests/test_shell_integration.py` passed (7/7 tests
passed).
* [x] Test B: Pyright static analysis on
`python_files/tests/test_shell_integration.py` completed with 0 errors
and 0 warnings.
* [x] Test C: Simulated platform check evaluation verifying
`sys.platform != "darwin"` evaluates to `True` on both Linux and
Windows.

## Checklist
- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my own code
- [x] I have commented my code, particularly in hard-to-understand areas
- [x] My changes generate no new warnings

Author: SatyamPandey-07

python_files/tests/test_shell_integration.py

@@ -119,7 +119,7 @@ def test_print_statement_darwin(monkeypatch):
             )
 
 
-if sys.platform == "win32":
+if sys.platform != "darwin":
 
     def test_print_statement_non_darwin(monkeypatch):
         importlib.reload(pythonrc)