mock pubmed API call in test

[proccaserra]

to avoid build failure as witnessed:

ERROR: test_get_pubmed_article (utils.test_isatools_utils.TestPubMedIDUtil)

Traceback (most recent call last):
File "/home/runner/work/isa-api/isa-api/tests/utils/test_isatools_utils.py", line 172, in test_get_pubmed_article
J = pubmed.get_pubmed_article('25520553')
File "/home/runner/work/isa-api/isa-api/isatools/net/pubmed.py", line 23, in get_pubmed_article
handle = Entrez.efetch(db="pubmed", id=pubmed_id.strip(), rettype="medline", retmode="text")
File "/opt/hostedtoolcache/Python/3.10.13/x64/lib/python3.10/site-packages/Bio/Entrez/init.py", line 197, in efetch
return _open(request)
File "/opt/hostedtoolcache/Python/3.10.13/x64/lib/python3.10/site-packages/Bio/Entrez/init.py", line 623, in _open
handle = urlopen(request)
File "/opt/hostedtoolcache/Python/3.10.13/x64/lib/python3.10/urllib/request.py", line 216, in urlopen
return opener.open(url, data, timeout)
File "/opt/hostedtoolcache/Python/3.10.13/x64/lib/python3.10/urllib/request.py", line 525, in open
response = meth(req, response)
File "/opt/hostedtoolcache/Python/3.10.13/x64/lib/python3.10/urllib/request.py", line 634, in http_response
response = self.parent.error(
File "/opt/hostedtoolcache/Python/3.10.13/x64/lib/python3.10/urllib/request.py", line 563, in error
return self._call_chain(*args)
File "/opt/hostedtoolcache/Python/3.10.13/x64/lib/python3.10/urllib/request.py", line 496, in _call_chain
result = func(*args)
File "/opt/hostedtoolcache/Python/3.10.13/x64/lib/python3.10/urllib/request.py", line 643, in http_error_default
raise HTTPError(req.full_url, code, msg, hdrs, fp)
urllib.error.HTTPError: HTTP Error 502: Bad Gateway