fix: requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-PILLOW-6219984
- https://snyk.io/vuln/SNYK-PYTHON-PILLOW-6219986

requirements.txt

@@ -1,4 +1,5 @@
 chardet>=4.0.0
 imageio>=2.9.0
 PyQt5>=5.15.4
-XlsxWriter>=3.0.1
+XlsxWriter>=3.0.1
+pillow>=10.2.0 # not directly required, pinned by Snyk to avoid a vulnerability