Harden workflows

[N-Wouda]

I ran zizmor over our workflows and fixed a few things it flagged.

Details

Notes:

Please read our contributing guidelines first.
In particular:

• You must add tests when making code changes.
  This keeps the code coverage level up, and helps ensure the changes work as intended.
• When fixing a bug, you must add a test that would produce the bug in the master branch, and then show that it is fixed with the new code.
• New code additions must be well formatted. Changes should pass the pre-commit workflow, which you can set up locally using pre-commit.
• Docstring additions must render correctly, including escapes and LaTeX.
• Finally, it is essential that all contributions in this PR are license-compatible with PyVRP's MIT license.
  Please check that this PR can be included into PyVRP under the MIT license.

[codspeed-hq]

CodSpeed Performance Report

Merging #670 will degrade performances by 76.71%

_{Comparing harden-ci-workflows (20ea258) with main (b5764a1)}

Summary

⚡ 8 improvements
❌ 23 regressions
✅ 11 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	main	harden-ci-workflows	Change
⚡	test_all_operators[mdvrp]	176.9 ms	149.6 ms	+18.2%
⚡	test_all_operators[vrpb]	19.7 ms	17.4 ms	+12.86%
❌	test_all_operators[vrptw]	18.6 ms	30.4 ms	-38.73%
❌	test_each_node_operator[mdvrp-Exchange20]	50.7 ms	56.4 ms	-10.16%
❌	test_each_node_operator[mdvrp-Exchange30]	40.5 ms	46.3 ms	-12.48%
⚡	test_each_node_operator[mdvrp-SwapTails]	76.1 ms	57.1 ms	+33.31%
❌	test_each_node_operator[vrpb-Exchange10]	6.9 ms	8.3 ms	-16.97%
❌	test_each_node_operator[vrpb-Exchange11]	905 µs	1,188.7 µs	-23.87%
❌	test_each_node_operator[vrpb-Exchange20]	538.6 µs	859.3 µs	-37.32%
❌	test_each_node_operator[vrpb-Exchange21]	541.4 µs	852.8 µs	-36.52%
❌	test_each_node_operator[vrpb-Exchange22]	539.2 µs	850.5 µs	-36.6%
❌	test_each_node_operator[vrpb-Exchange30]	541.4 µs	858.6 µs	-36.94%
❌	test_each_node_operator[vrpb-Exchange31]	540.9 µs	848.3 µs	-36.24%
❌	test_each_node_operator[vrpb-Exchange32]	538.8 µs	848.5 µs	-36.51%
❌	test_each_node_operator[vrpb-Exchange33]	539.3 µs	849 µs	-36.48%
❌	test_each_node_operator[vrpb-SwapTails]	4.3 ms	5.3 ms	-19.08%
⚡	test_each_node_operator[vrptw-Exchange10]	6.8 ms	6 ms	+12.25%
❌	test_each_node_operator[vrptw-Exchange11]	3.9 ms	5 ms	-21%
❌	test_each_node_operator[vrptw-Exchange20]	5.5 ms	7.8 ms	-28.94%
⚡	test_each_node_operator[vrptw-Exchange21]	5.4 ms	4.8 ms	+13.85%
...	...	...	...	...

ℹ️ Only the first 20 benchmarks are displayed. Go to the app to view all benchmarks.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.69%. Comparing base (e0df3ff) to head (20ea258).
Report is 41 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #670   +/-   ##
=======================================
  Coverage   96.69%   96.69%           
=======================================
  Files          76       76           
  Lines        3661     3663    +2     
  Branches      945      947    +2     
=======================================
+ Hits         3540     3542    +2     
  Misses         13       13           
  Partials      108      108           

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