fix: Dockerfile.python.drf_ms_pg to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-ALPINE312-BUSYBOX-1089799
- https://snyk.io/vuln/SNYK-ALPINE312-BUSYBOX-1089799
- https://snyk.io/vuln/SNYK-ALPINE312-OPENSSL-1075735
- https://snyk.io/vuln/SNYK-ALPINE312-OPENSSL-1089238
- https://snyk.io/vuln/SNYK-ALPINE312-OPENSSL-1089238

Dockerfile.python.drf_ms_pg

@@ -1,4 +1,4 @@
-FROM python:3.8.3-alpine
+FROM python:3-alpine
 
 # PYTHONDONTWRITEBYTECODE: Prevents Python from writing pyc files to disc (equivalent to python -B option)
 # PYTHONUNBUFFERED: Prevents Python from buffering stdout and stderr (equivalent to python -u option)