Remove deprecated python 3.8

[alkino]

No description provided.

[azure-pipelines]

✔️ 4e2d2a4 -> Azure artifacts URL

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.07%. Comparing base (1e95ecc) to head (f887ea2).
Report is 4 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3108   +/-   ##
=======================================
  Coverage   67.07%   67.07%           
=======================================
  Files         569      569           
  Lines      111206   111206           
=======================================
  Hits        74592    74592           
  Misses      36614    36614           

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[azure-pipelines]

✔️ d006dec -> Azure artifacts URL

[azure-pipelines]

✔️ d818938 -> Azure artifacts URL

[JCGoran]

3.8 is officially EOL as of today, we can merge this.

[1uc]

Is there anything we're currently interested in that's failing only for Python 3.8? If not, I'd say continue to check until it breaks.

[JCGoran]

Not sure if related, but CircleCI fails on 3.8: https://app.circleci.com/pipelines/github/neuronsimulator/nrn/9697/workflows/fabca25f-f7da-4e81-b0f3-bef12f3bf368/jobs/4732
If we try 3.9, it works: https://app.circleci.com/pipelines/github/neuronsimulator/nrn/9714/workflows/fafc7f8d-9aa2-4638-98ab-8d618269d670/jobs/4736 (from this PR: #3197; also tried with RDMAV_FORK_SAFE=1, but it didn't do anything on 3.8).

I haven't found any mention of 3.8 being an issue on CircleCI, so it could just be a coincidence, but having one less Python version to support is always nice.

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[azure-pipelines]

✔️ f887ea2 -> Azure artifacts URL

[bbpbuildbot]

Logfiles from GitLab pipeline #238237 (:white_check_mark:) have been uploaded here!

Status and direct links:

• ✅ mac_m1_cmake_build: [cmake, ON, OFF, OFF, address]
• ✅ spack_setup
• ✅ build:nmodl
• ✅ build:neuron:nmodl:intel:legacy
• ✅ build:neuron:nmodl:intel:shared
• ✅ build:neuron:nmodl:nvhpc:acc:legacy
• ✅ build:neuron:nmodl:nvhpc:acc:shared
• ✅ build:neuron:nmodl:nvhpc:omp:legacy
• ✅ build:neuron:nmodl:nvhpc:omp
• ✅ test:neuron:nmodl:intel:legacy
• ✅ test:neuron:nmodl:intel:shared
• ✅ test:neuron:nmodl:nvhpc:acc:legacy
• ✅ test:neuron:nmodl:nvhpc:acc:shared
• ✅ test:neuron:nmodl:nvhpc:omp:legacy
• ✅ test:neuron:nmodl:nvhpc:omp