Fix spelling errors identified by codespell 1.15.0

After this commit, the only remaining output is:

  $ test/lint/lint-spelling.sh
  src/test/base32_tests.cpp:14: fo  ==> of, for
  src/test/base64_tests.cpp:14: fo  ==> of, for
  ^ Warning: codespell identified likely spelling errors. Any false positives? Add them to the list of ignored words in test/lint/lint-spelling.ignore-words.txt

Note:
* I ignore several valid alternative spellings
* homogenous is present in tinyformat, hence should be addressed upstream
* process' is correct only if there are plural processes

test/lint/lint-spelling.ignore-words.txt

@@ -5,3 +5,10 @@ mut
 objext
 unselect
 useable
+wit
+unparseable
+copyable
+cachable
+errorstring
+keyserver
+homogenous