Fix failing test on OpenBSD

[bket]

A borgbackup-2.0.0b6 test fails on OpenBSD with the message below.

=================================== FAILURES ===================================
_____________________________ test_get_runtime_dir _____________________________

path = '/run/user/55/borg', mode = 511, pretty_deadly = True

    def ensure_dir(path, mode=stat.S_IRWXU | stat.S_IRWXG | stat.S_IRWXO, pretty_deadly=True):
        """
        Ensures that the dir exists with the right permissions.
        1) Make sure the directory exists in a race-free operation
        2) If mode is not None and the directory has been created, give the right
        permissions to the leaf directory. The current umask value is masked out first.
        3) If pretty_deadly is True, catch exceptions, reraise them with a pretty
        message.
        Returns if the directory has been created and has the right permissions,
        An exception otherwise. If a deadly exception happened it is reraised.
        """
        try:
>           os.makedirs(path, mode=mode, exist_ok=True)

build/lib.openbsd-7.3-amd64-cpython-310/borg/helpers/fs.py:37:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

If $XDG_RUNTIME_DIR is not set platformdirs.user_runtime_dir() returns one of 3 different paths
(tox-dev/platformdirs#201). Proposed fix is to check if get_runtime_dir() returns one of these paths.

Supersedes #7652.

[codecov-commenter]

Codecov Report

Merging #7719 (1074089) into master (616d5e7) will decrease coverage by 0.12%.
The diff coverage is n/a.

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@@            Coverage Diff             @@
##           master    #7719      +/-   ##
==========================================
- Coverage   83.86%   83.75%   -0.12%     
==========================================
  Files          66       66              
  Lines       11864    11900      +36     
  Branches     2149     2155       +6     
==========================================
+ Hits         9950     9967      +17     
- Misses       1345     1360      +15     
- Partials      569      573       +4     

see 8 files with indirect coverage changes

[ThomasWaldmann]

Thanks!