Drop support for GCC < 8
GCC 7 is no longer supported upstream, so we should stop building for it. The build platforms provide the following versions
- conda-forge: 12
- Debian Bookworm: 12 (gcc-11 available)
- RL8: 8
- RL9: 11
GCC 7 is no longer supported upstream, so we should stop building for it. The build platforms provide the following versions