fix: docker/Dockerfile.clang12 to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-UBUNTU2310-GCC13-5972626
- https://snyk.io/vuln/SNYK-UBUNTU2310-GLIBC-5972086
- https://snyk.io/vuln/SNYK-UBUNTU2310-GLIBC-5972086
- https://snyk.io/vuln/SNYK-UBUNTU2310-GLIBC-5972275
- https://snyk.io/vuln/SNYK-UBUNTU2310-XZUTILS-5988806

docker/Dockerfile.clang12

@@ -27,7 +27,7 @@ RUN cmake -D$target=ON -DBUILD_CMD_LINE_TOOLS=ON -DBUILD_DEMONSTRATION=OFF .. &&
 # RELEASE stage
 #FROM alpine:latest as release    # hitting a segfault during startup of some playground programs
 #FROM debian:buster-slim as release
-FROM ubuntu:mantic-20230912 as release
+FROM ubuntu:mantic-20231011 as release
 LABEL Theodore Omtzigt
 
 #RUN apk add --no-cache libc6-compat libstdc++ cmake make bash gawk sed grep bc coreutils