templatekw: fix shownames() to check if namespace exists in repo (issue6301)
Namespace registration is dynamic, but the corresponding template keyword
is registered statically.
[tool.black]
line-length = 80
exclude = '''
build/
| wheelhouse/
| dist/
| packages/
| \.hg/
| \.mypy_cache/
| \.venv/
| mercurial/thirdparty/
'''
skip-string-normalization = true
quiet = true