tests: Avoid using match of pytest.raises together with paths

[xdustinface]

Fixes failures like below. See https://github.com/Chia-Network/chia-blockchain/actions/runs/2386606563 for a test run against #10681.

______________________ test_harvester_add_plot_directory 
______________________
[gw1] win32 -- Python 3.7.9 
d:\a\chia-blockchain\chia-blockchain\venv\scripts\python.exe
tests\core\test_farmer_harvester_rpc.py:573: in 
test_harvester_add_plot_directory
    await harvester_rpc_client.add_plot_directory(str(test_path))
chia\rpc\harvester_rpc_client.py:25: in add_plot_directory
    return (await self.fetch("add_plot_directory", {"dirname": 
dirname}))["success"]
chia\rpc\rpc_client.py:49: in fetch
    raise ValueError(res_json)
E   ValueError: {'error': "Path doesn't exist: 
C:\\Users\\runneradmin\\AppData\\Local\\Temp\\pytest-of-runneradmin\\pytest-0\\popen-gw1\\test_harvester_add_plot_direct0\\harvester\\test_path", 
'success': False}

During handling of the above exception, another exception occurred:
tests\core\test_farmer_harvester_rpc.py:573: in 
test_harvester_add_plot_directory
    await harvester_rpc_client.add_plot_directory(str(test_path))
C:\hostedtoolcache\windows\Python\3.7.9\x64\lib\re.py:185: in search
    return _compile(pattern, flags).search(string)
C:\hostedtoolcache\windows\Python\3.7.9\x64\lib\re.py:288: in _compile
    p = sre_compile.compile(pattern, flags)
C:\hostedtoolcache\windows\Python\3.7.9\x64\lib\sre_compile.py:764: in 
compile
    p = sre_parse.parse(p, flags)
C:\hostedtoolcache\windows\Python\3.7.9\x64\lib\sre_parse.py:924: in 
parse
    p = _parse_sub(source, pattern, flags & SRE_FLAG_VERBOSE, 0)
C:\hostedtoolcache\windows\Python\3.7.9\x64\lib\sre_parse.py:420: in 
_parse_sub
    not nested and not items))
C:\hostedtoolcache\windows\Python\3.7.9\x64\lib\sre_parse.py:501: in 
_parse
    code = _escape(source, this, state)
C:\hostedtoolcache\windows\Python\3.7.9\x64\lib\sre_parse.py:369: in 
_escape
    raise source.error("incomplete escape %s" % escape, len(escape))
E   re.error: incomplete escape \U at position 22