test_email: test_localtime_daylight_false_dst_true() fails if timezone database is missing

[5bd1ef4d-0732-4943-a379-4af489e20c69]

BPO	35818
Nosy	@warsaw, @vstinner, @bitdancer, @andreas-schwab, @pganssle, @miss-islington, @tirkarthi

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields: ```python assignee = None closed_at = None created_at = labels = ['3.8', 'type-bug', '3.7'] title = 'test_email: test_localtime_daylight_false_dst_true() fails if timezone database is missing' updated_at = user = 'https://github.com/andreas-schwab' ``` bugs.python.org fields: ```python activity = actor = 'schwab' assignee = 'none' closed = False closed_date = None closer = None components = [] creation = creator = 'schwab' dependencies = [] files = [] hgrepos = [] issue_num = 35818 keywords = [] message_count = 3.0 messages = ['334294', '334296', '334297'] nosy_count = 7.0 nosy_names = ['barry', 'vstinner', 'r.david.murray', 'schwab', 'p-ganssle', 'miss-islington', 'xtreak'] pr_nums = [] priority = 'normal' resolution = None stage = None status = 'open' superseder = None type = 'behavior' url = 'https://bugs.python.org/issue35818' versions = ['Python 3.6', 'Python 3.7', 'Python 3.8'] ```

[5bd1ef4d-0732-4943-a379-4af489e20c69]

bpo-35317 solution is incomplete, the test needs to be skipped if the timezone database is unavailable.

[vstinner]

How can I reproduce the issue?

[5bd1ef4d-0732-4943-a379-4af489e20c69]

rpm -e timezone