Trigger test workflows on master pushes

[mickaelbegon]

Summary

• Trigger the Linux test workflow on pushes to master in addition to pull requests.
• Trigger the macOS/Windows test workflow on pushes to master in addition to pull requests.

Why

The README CI badge points to the Linux test workflow, but the workflow only ran for pull requests. Since the repository default branch is master, completed merges did not refresh the badge status for the default branch.

Fixes #1060.

Validation

• git diff --check

---

This change is 

[codecov]

Codecov Report

❌ Patch coverage is 60.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.26%. Comparing base (627c167) to head (79348c2).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
bioptim/gui/ipopt_output_plot.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1061      +/-   ##
==========================================
- Coverage   77.26%   77.26%   -0.01%     
==========================================
  Files         196      196              
  Lines       21508    21505       -3     
==========================================
- Hits        16618    16615       -3     
  Misses       4890     4890              

Flag	Coverage Δ
unittests	77.26% <60.00%> (-0.01%)	⬇️

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