SPI-2550: LCG_104d_ATLAS_15/16, new layers with flake8 and friends
New layers LCG_104d_ATLAS_15_16 with:
- flake8-7.0.0
- flake8_builtins-2.5.0
- flake8_bugbear-24.2.6
- pycodestyle-2.11.1
- pyflakes-3.2.0
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New layers LCG_104d_ATLAS_15_16 with: