Automatic merge from submit-queue

oidc authentication plugin: don't trim issuer URLs with trailing slashes

The issuer URL passed to the plugin must identically match the issuer
URL returned by OpenID Connect discovery. However, the plugin currently
trims all trailing slashes from issuer URLs, causing a mismatch. Since
the go-oidc client already handles this case correctly, don't trim the
path.

Closes #29749

cc @hanikesn @kubernetes/sig-auth