CompatHelper: bump compat for "Observables" to "0.3"

[github-actions]

This pull request changes the compat entry for the Observables package from 0.2.3 to 0.2.3, 0.3.

This keeps the compat entries for earlier versions.

Note: I have not tested your package with this new compat entry. It is your responsibility to make sure that your package tests pass before you merge this pull request.

[codecov-io]

Codecov Report

Merging #3 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master       #3   +/-   ##
=======================================
  Coverage   93.75%   93.75%           
=======================================
  Files           2        2           
  Lines          16       16           
=======================================
  Hits           15       15           
  Misses          1        1

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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.75%. Comparing base (54ec058) to head (f7bbc16).
Report is 19 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master       #3   +/-   ##
=======================================
  Coverage   93.75%   93.75%           
=======================================
  Files           2        2           
  Lines          16       16           
=======================================
  Hits           15       15           
  Misses          1        1           

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