Add a linter to check the images' alt text (#63) (#66)

* Create linter and allowlist

* refactor linter and add it to CI

* refactor loop

* use VCS to install the linter

* Skip invalid image

* Small fix of the linter

(cherry picked from commit 1996a0d)

Co-authored-by: Arnau Casau <47946624+arnaucasau@users.noreply.github.com>

Author: mergify[bot]

tox.ini

@@ -21,6 +21,9 @@ commands =
   nbqa ruff --fix docs/
 
 [testenv:lint]
+image-tester-commit = 7ae965ccf21c39e5170334ec7f4882756883860a
+deps = 
+  git+https://github.com/Qiskit/documentation.git@{[testenv:lint]image-tester-commit}\#egg=sphinx-alt-text-validator&subdirectory=scripts/image-tester
 basepython = python3.10
 extras =
   lint
@@ -31,6 +34,7 @@ commands =
   nbqa ruff docs/
   mypy qiskit_addon_utils/
   pylint -rn qiskit_addon_utils/ test/
+  sphinx-alt-text-validator -f qiskit_addon_utils -s qiskit_addon_utils/problem_generators/generate_time_evolution_circuit.py
   nbqa pylint -rn docs/
   typos
   reno lint