fix: ensure submodule files are included with --recurse-submodules

[sentry]

The --recurse-submodules option in codecov-cli was not correctly including files from Git submodules if those submodules were not explicitly initialized (e.g., via git submodule update --init). This caused an AssertionError in validation tests, as git ls-files --recurse-submodules only lists files from initialized submodules.

This fix modifies GitVersioningSystem.list_relevant_files to automatically run git submodule update --init --recursive before executing git ls-files --recurse-submodules. This ensures that all submodules are properly initialized, allowing git ls-files to correctly enumerate their contents. A warning is logged if the submodule update command fails, preventing hard failures in scenarios where submodules might not be present or accessible.

Fixes CLI-GD

_{This PR was automatically generated by Sentry. You can adjust this setting at any time.}

[codecov]

❌ 1 Tests Failed:

Tests completed	Failed	Passed	Skipped
723	1	722	1

View the full list of 1 ❄️ flaky test(s)

api.temp.calculator.test_calculator::test_divide

Flake rate in main: 100.00% (Passed 0 times, Failed 1726 times)

Stack Traces | 0.001s run time

def
                test_divide():
                > assert Calculator.divide(1, 2) == 0.5
                E assert 1.0 == 0.5
                E + where 1.0 = <function Calculator.divide at 0x104c9eb90>(1, 2)
                E + where <function Calculator.divide at 0x104c9eb90> = Calculator.divide
                .../temp/calculator/test_calculator.py:30: AssertionError

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