Fixup changelog and write live config content when updating it

[gaborbernat]

👍

[codecov]

Codecov Report

Merging #1006 into master will decrease coverage by 0.99%.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master    #1006   +/-   ##
=======================================
- Coverage   70.45%   69.45%   -1%     
=======================================
  Files          14       14           
  Lines        3479     3483    +4     
  Branches      465      465           
=======================================
- Hits         2451     2419   -32     
- Misses        967     1002   +35     
- Partials       61       62    +1

Impacted Files	Coverage Δ
src/tox/_pytestplugin.py	81.42% <ø> (ø)	⬆️
src/tox/venv.py	78.58% <100%> (-1.37%)	⬇️
src/tox/interpreters.py	64.74% <0%> (-17.99%)	⬇️
src/tox/session.py	77.86% <0%> (-0.32%)	⬇️
src/tox/config.py	65.05% <0%> (-0.16%)	⬇️

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