build env: workarounds for conda issues on linux

first issue here:
conda/conda-libmamba-solver#283

-> adding libarchive and libmamba from *same* channel

(only saw the problem with Python 3.12)

envs/linux/conda/environment-py3.12.yml

@@ -2,6 +2,8 @@ channels:
   - defaults
 dependencies:
   - python=3.12
+  - anaconda::libarchive
+  - anaconda::libmamba
   - anaconda::conda-build
   - anaconda::conda-verify
   - anaconda::sphinx