[README] Fix github actions badge

[davidor]

What does this PR do?

Fixes the github actions badge. The action-badges.now.sh that we were using only works for repos that use the master branch

[github-actions]

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[codecov-commenter]

Codecov Report

Merging #366 (cca7a2e) into main (96b8e73) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #366   +/-   ##
=======================================
  Coverage   65.04%   65.04%           
=======================================
  Files          63       63           
  Lines        6901     6901           
=======================================
  Hits         4489     4489           
  Misses       2093     2093           
  Partials      319      319           

Flag	Coverage Δ
unittests	65.04% <ø> (ø)

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