remove pin to outdated debian buster; improve test comparator

Dockerfile

@@ -1,4 +1,4 @@
-FROM python:3-slim-buster as builder
+FROM python:3-slim as builder
 
 LABEL description="ElastAlert 2 Official Image"
 LABEL maintainer="Jason Ertel"
@@ -10,7 +10,7 @@ RUN mkdir -p /opt/elastalert && \
     pip install setuptools wheel && \
     python setup.py sdist bdist_wheel
 
-FROM python:3-slim-buster
+FROM python:3-slim
 
 ARG GID=1000
 ARG UID=1000

tests/Dockerfile-test

@@ -1,4 +1,4 @@
-FROM python:3-slim-buster
+FROM python:3-slim
 
 RUN apt update && apt upgrade -y
 RUN apt install -y gcc libffi-dev

tests/auth_test.py

@@ -38,5 +38,5 @@ def test_auth_aws_region():
         profile_name=None
     )
 
-    assert type(auth) == RefeshableAWSRequestsAuth
+    assert type(auth) is RefeshableAWSRequestsAuth
     assert auth.aws_region == 'us-east-1'