Avoid to update conda base environment with the defaults channel.

Signed-off-by: Daniel Scheffler <danschef@gfz-potsdam.de>
6 jobs for master in 2 minutes and 7 seconds (queued for 2 seconds)
Status Name Job ID Coverage
  Test
passed test_py_tools_ds #40460

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passed test_py_tools_ds_install #39500

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passed test_styles #39499

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passed test_py_tools_ds #39498

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63.0%
 
  Deploy Pages
passed pages #39501

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  Deploy
passed pages:deploy

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