fix: requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-PILLOW-6182918

requirements.txt

@@ -36,7 +36,7 @@ Markdown==3.4.4
 mysqlclient==2.1.1
 openpyxl==3.1.2
 xlrd==1.2.0
-Pillow==10.0.0  # required by django-imagekit
+Pillow==10.2.0  # required by django-imagekit
 psycopg2-binary==2.9.6
 cryptography==41.0.3
 python-dateutil==2.8.2