fix: add email query to github idp if email empty (#10705)

# Which Problems Are Solved

In the integration with Github, private emails are not returned with the
userinfo.

# How the Problems Are Solved

If the scope `user:email` is set in the Github IDP and the email is not
included in the userinfo, a request to Github's API is executed to query
the email of the user.

# Additional Changes

Additional tests.

# Additional Context

Closes #10098

---------

Co-authored-by: Marco A. <[email protected]>
Co-authored-by: Livio Spring <[email protected]>

internal/idp/providers/github/github.go

@@ -13,10 +13,11 @@ import (
 )
 
 const (
-	authURL    = "https://github.com/login/oauth/authorize"
-	tokenURL   = "https://github.com/login/oauth/access_token"
-	profileURL = "https://api.github.com/user"
-	name       = "GitHub"
+	authURL        = "https://github.com/login/oauth/authorize"
+	tokenURL       = "https://github.com/login/oauth/access_token"
+	profileURL     = "https://api.github.com/user"
+	emailURLSuffix = "/emails"
+	name           = "GitHub"
 )
 
 var _ idp.Provider = (*Provider)(nil)
@@ -43,12 +44,14 @@ func NewCustomURL(name, clientID, secret, callbackURL, authURL, tokenURL, profil
 	}
 	return &Provider{
 		Provider: rp,
+		emailURL: profileURL + emailURLSuffix,
 	}, nil
 }
 
 // Provider is the [idp.Provider] implementation for GitHub
 type Provider struct {
 	*oauth.Provider
+	emailURL string
 }
 
 func newConfig(clientID, secret, callbackURL, authURL, tokenURL string, scopes []string) *oauth2.Config {