Bump minimum python version

.gitlab-ci.yml

.pre-commit-config.yaml

bilby/bilby_mcmc/chain.py

bilby/bilby_mcmc/proposals.py

bilby/bilby_mcmc/sampler.py

bilby/gw/detector/interferometer.py

bilby/gw/detector/networks.py

containers/v3-dockerfile-test-suite-python37

containers/write_dockerfiles.py

examples/core_examples/radioactive_decay.py

setup.py

test/core/sampler/pymc3_test.py

test/gw/detector/interferometer_test.py

test/gw/detector/networks_test.py

test/integration/sampler_run_test.py