Fix bug related to holoviews test

[dachengx]

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What does the code in this PR do / what does it improve?

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Can you give a minimal working example (or illustrate with a figure)?

Please include the following if applicable:

• Update the docstring(s)
• Update the documentation
• Tests to check the (new) code is working as desired.
• Does it solve one of the open issues on github?

Notes on testing

• Until the automated tests pass, please mark the PR as a draft.
• On the XENONnT fork we test with database access, on private forks there is no database access for security considerations.

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[coveralls]

coverage: 89.799% (+0.02%) from 89.777%
when pulling 46abb45 on bug_fix_holoviews
into 0c44889 on master.