fix: Dockerfile to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-DEBIAN10-SYSTEMD-3339153
- https://snyk.io/vuln/SNYK-DEBIAN10-SYSTEMD-3339153
- https://snyk.io/vuln/SNYK-DEBIAN10-OPENSSL-2426310
- https://snyk.io/vuln/SNYK-DEBIAN10-OPENSSL-2807585
- https://snyk.io/vuln/SNYK-DEBIAN10-OPENSSL-2807585

Author: snyk-bot

Dockerfile

@@ -1,6 +1,6 @@
 ## Use latest slim Python image. Note that it's built on Debian Stretch.
 # `python-base` sets up all our shared environment variables
-FROM python:3.8.1-slim as python-base
+FROM python:3.14.0rc2-slim as python-base
 
 ARG GRIDAPPSD_PYTHON_VERSION