fix: cvat/requirements/base.txt to reduce vulnerabilities (#4131)

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-PILLOW-2331901
- https://snyk.io/vuln/SNYK-PYTHON-PILLOW-2331905
- https://snyk.io/vuln/SNYK-PYTHON-PILLOW-2331907

cvat/requirements/base.txt

@@ -7,7 +7,7 @@ django-cacheops==5.0.1
 django-compressor==2.4
 django-rq==2.3.2
 EasyProcess==0.3
-Pillow==8.3.2
+Pillow==9.0.0
 numpy==1.19.5
 python-ldap==3.4.0
 pytz==2020.1