Update Dockerfile base image to use bullseye instead of bookworm

[0x4r45h]

Describe your changes

The updated Dockerfile in #2687 implicitly uses Debian Bookworm instead of Bullseye, which causes the following issues:

1. it doesn't have clang-tools-11
2. it is inconsistence with the base image used by namada-wasm Dockerfile which explicitly uses bullseye image

Indicate on which release or other PRs this topic is based on

Fixes https://github.com/anoma/namada/actions/runs/8192271541/job/22403401963

Checklist before merging to draft

• I have added a changelog
• Git history is in acceptable state

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 53.88%. Comparing base (2ba001d) to head (346766a).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2847   +/-   ##
=======================================
  Coverage   53.88%   53.88%           
=======================================
  Files         308      308           
  Lines      100154   100154           
=======================================
+ Hits        53966    53967    +1     
+ Misses      46188    46187    -1     

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