make cf standard name validation robust to URL errors

[d-v-b]

validating cf standard names requires fetching a standard name table from github, but when working offline that's not possible. This PR adds a fallback (no name validation) when a URL error is raised when fetching the cf standard name table, which makes it possible to work on the package offline.

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Codecov Report

❌ Patch coverage is 73.33333% with 4 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/eopf_geozarr/data_api/geozarr/common.py	73.33%	4 Missing ⚠️

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[emmanuelmathot]

@d-v-b This ws included in #75 as well right? We can close?

[d-v-b]

@d-v-b This ws included in #75 as well right? We can close?

yes this went in already. closing