Re-enable unit test as server issue is resolved.

[PGijsbers]

With OpenML#980 closed, we can re-enable this unit test which failed due to server-side issues.

[codecov-io]

Codecov Report

Merging #761 into develop will increase coverage by 0.86%.
The diff coverage is n/a.

@@ Coverage Diff @@## develop #761 +/- ##
===========================================
+ Coverage 87.72% 88.58% +0.86% 
===========================================
Files 36 36 Lines 4072 4556 +484 ===========================================
+ Hits 3572 4036 +464 - Misses 500 520 +20

Impacted Files	Coverage Δ
openml/_api_calls.py	83.11% <0%> (-1.3%)	⬇️
openml/utils.py	91.13% <0%> (-0.64%)	⬇️
openml/evaluations/functions.py	92.23% <0%> (-0.08%)	⬇️
openml/flows/functions.py	88.69% <0%> (+0.72%)	⬆️
openml/extensions/sklearn/extension.py	93.43% <0%> (+2.08%)	⬆️

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