Fix typos discovered by codespell

[cclauss]

• https://pypi.org/project/codespell
• https://github.com/codespell-project/codespell

% codespell --ignore-words-list=assertin,crasher,ehr,fallin,fo,minggw,re-use,seh,ths,windowz

./CHANGES.rst:184: interpeter ==> interpreter
./src/greenlet/TThreadStateDestroy.cpp:125: happenend ==> happened
./src/greenlet/greenlet.cpp:1223: Debbuging ==> Debugging

% codespell --ignore-words-list=assertin,crasher,ehr,fallin,fo,minggw,re-use,seh,ths,windowz --write-changes

Also, Python 3.7 was already end-of-life when Apple Silicon was released so Python 3.7 is not supported on modern Macs.

[jamadden]

Thank you, this was fixed in a different manner.