Improve validation for format parameter in Oembed request

[edlib-oddarne]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 42.94%. Comparing base (94429d6) to head (d91d444).
⚠️ Report is 2 commits behind head on master.

❗ There is a different number of reports uploaded between BASE (94429d6) and HEAD (d91d444). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (94429d6)	HEAD (d91d444)
	2	1

Additional details and impacted files

@@              Coverage Diff              @@
##             master    #3273       +/-   ##
=============================================
- Coverage     61.01%   42.94%   -18.08%     
+ Complexity     3587      946     -2641     
=============================================
  Files           410      171      -239     
  Lines         15590     3754    -11836     
=============================================
- Hits           9513     1612     -7901     
+ Misses         6077     2142     -3935     

Components	Coverage Δ
Content Author	∅ <ø> (∅)
Hub	42.94% <100.00%> (-0.05%)	⬇️

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