docs: fix openid-connect documentation typos

Fixed typos in openid-connect documentation No code change

[X] I have explained the need for this PR and the problem it solves
[X] I have explained the changes or the new features added to this PR
[X] I have added tests corresponding to this change
[X] I have updated the documentation to reflect this change
[X] I have verified that this change is backward compatible (If not, please discuss on the APISIX mailing list first)

apache / apisix