File size of dummy.dummy.txt on windows might be 5 or 6 bytes

[brawner]

In PR #197, the TestFilesystemFixture.calculate_file_size test checks the file size of a small text file containing the string "ROS2". Because of windows-style line-endings and how git automatically corrects them, this file is actually 6 bytes when checked out with git, but 5 bytes when directly downloaded from gist.

Example of test failure
https://citest.ros2.org/job/ci_windows/116/testReport/rcutils/TestFilesystemFixture/

[brawner]

@Karsten1987

[Karsten1987]

Thanks @brawner for reporting this. I somehow ignored to run tests for rcutils when introducing the change for rosbags. I'll work on a correction.