SAML/SCIM API :uid parameter unable to handle periods

Summary

Related to #98354, customers are unable to update SAML/SCIM extern_uid via API when the current value includes a period. e.g. value is an email

Steps to reproduce

1. Assign an identity to a user that includes a period
2. Make a PATCH request to the groups/:groups_id/saml/:uid endpoint to update the users identity

What is the current bug behavior?

Due to the period, it is unable to find the identity and errors out with a 404.

What is the expected correct behavior?

Successful response showing the updated extern_uid and user_id

Relevant logs and/or screenshots

Unsuccessful with period:

curl --location --request PATCH "https://gitlab.com/api/v4/groups/58946864/saml/test+test@gitlab.com" --header 'PRIVATE-TOKEN: token' --form 'extern_uid=test'
{"message":"404 Identity Not Found"}

Successful without period:

curl --location --request PATCH "https://gitlab.com/api/v4/groups/58946864/saml/test+test@gitlabcom" --header 'PRIVATE-TOKEN: token' --form 'extern_uid=test'
{"extern_uid":"test","user_id":8278845}

Possible fixes

https://gitlab.com/gitlab-org/gitlab/-/blob/master/ee/lib/api/provider_identity.rb#L45