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>

certbot-compatibility-test/nginx/nginx-roundtrip-testdata/piwik/nginx.conf

@@ -24,7 +24,7 @@ server {
 
     # Disallow any usage of piwik assets if referer is non valid.
     location ~* ^.+\.(?:jpg|png|css|gif|jpeg|js|swf)$ {
-             # Defining the valid referers.
+             # Defining the valid referrers.
              valid_referers none blocked *.mysite.com othersite.com;
              if ($invalid_referer)  {
                 return 444;