fix: gracefully handle missing files during coverage upload

[sentry]

This PR addresses an issue where the codecov-cli would crash with a FileNotFoundError during a coverage upload if a file tracked by git was not present on the local filesystem. This commonly occurs with generated files (e.g., *.g.dart in Flutter projects) that are committed to version control but might not be generated in a specific local environment.

The root cause was that the _get_file_fixes function in codecov_cli/services/upload/upload_collector.py attempted to open such files without handling FileNotFoundError.

This fix adds an except FileNotFoundError block to _get_file_fixes. Now, if a git-tracked file is not found on disk, a warning will be logged, and the file will be skipped, allowing the coverage upload process to complete without interruption. This approach aligns with the existing error handling for UnicodeDecodeError and IsADirectoryError in the same function.

Fixes CLI-GS

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[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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