CI: ansible_tests.py sets incorrect, world readable/writable, permissions on SSH key mitogen__has_sudo_pubkey.key

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The wrong base is used when calculating the mode in

mitogen/.ci/ansible_tests.py

Lines 42 to 44 in a35b208

	with ci_lib.Fold('job_setup'):
	os.chdir(TESTS_DIR)
	os.chmod('../data/docker/mitogen__has_sudo_pubkey.key', int('0600', 7))

it should be base 8. The correct permission is u=rw,g=,o=, the actual result is 0o446 -> u=r,g=r,o=rw.
This key is only used during CI jobs, so I don't think this bug results in a security vulnerability of mitogen. The incorrect permission was introduced in commit 06ae597#diff-2b989045c3f414fc662f679fc29531d94bfb5f614f793af91913c5dfa6b2c578R32-R34 on Aug 18 2018 when the script was converted from Bash to Python.

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The key in question is stored in git https://github.com/mitogen-hq/mitogen/blob/master/tests/data/docker/mitogen__has_sudo_pubkey.key