Add codespell support (CI to check, not to fix) and make it fix a few typos (#10297)

Another token of gratitude for a super useful tool and service.

More about codespell: https://github.com/codespell-project/codespell .

I personally introduced it to dozens if not hundreds of projects already
and so far only positive feedback.

CI workflow has 'permissions' set only to 'read' so also should be safe.

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Signed-off-by: Yaroslav O. Halchenko <debian@onerussian.com>

letsencrypt-auto-source/letsencrypt-auto

@@ -162,7 +162,7 @@ SuSudo() {
 }
 
 # Sets the environment variable SUDO to be the name of the program or function
-# to call to get root access. If this script already has root privleges, SUDO
+# to call to get root access. If this script already has root privileges, SUDO
 # is set to an empty string. The value in SUDO should be run with the command
 # to called with root privileges as arguments.
 SetRootAuthMechanism() {