.napari/DESCRIPTION.md and CITATION.cff required when using napari-hub-preview-action

[Czaki]

Description

When .napari/DESCRIPTION.md orCITATION.cffis missed then napari-hub-preview-action fail with FileNotFoundError

https://github.com/4DNucleome/PartSeg/runs/4684547184?check_suite_focus=true#step:3:538

Steps/Code to Reproduce

Source of problem is not checking if file exists before try to open it:

napari-hub/backend/utils/github.py

Lines 49 to 52 in e2ee13d

	if local_workspace:
	# read files locally since github action already checked it out
	with open(os.path.join(local_workspace, file)) as f:
	return f.read()

The get_file function is called here:

napari-hub/backend/utils/github.py

Line 118 in e2ee13d

description = get_file(repo_url, ".napari/DESCRIPTION.md", branch=branch)

and

napari-hub/backend/utils/github.py

Line 123 in e2ee13d

citation_file = get_file(repo_url, "CITATION.cff", branch=branch)

Expected Results

Files should be optional:
4DNucleome/PartSeg#489 (comment)

Actual Results

 Traceback (most recent call last):
  File "napari-hub/backend/get_preview.py", line 17, in <module>
    get_plugin_preview(repo_pth, dest_pth, args.local, args.branch)
  File "/home/runner/work/PartSeg/PartSeg/napari-hub/backend/preview/preview.py", line 48, in get_plugin_preview
    github_metadata = get_github_metadata(action_repo_url, branch=branch)
  File "/home/runner/work/PartSeg/PartSeg/napari-hub/backend/utils/github.py", line 118, in get_github_metadata
    description = get_file(repo_url, ".napari/DESCRIPTION.md", branch=branch)
  File "/home/runner/work/PartSeg/PartSeg/napari-hub/backend/utils/github.py", line 51, in get_file
    with open(os.path.join(local_workspace, file)) as f:
FileNotFoundError: [Errno 2] No such file or directory: '/home/runner/work/PartSeg/PartSeg/.napari/DESCRIPTION.md'

@neuromusic

[neuromusic]

fixed in #381