Increase the size of the webauthn_credential credential_id field (#18739)

Unfortunately credentialIDs in u2f are 255 bytes long which with base32 encoding
becomes 408 bytes. The default size of a xorm string field is only a VARCHAR(255)

This problem is not apparent on SQLite because strings get mapped to TEXT there.

Fix #18727

Signed-off-by: Andrew Thornton <art27@cantab.net>

models/migrations/v208.go

@@ -15,7 +15,7 @@ func useBase32HexForCredIDInWebAuthnCredential(x *xorm.Engine) error {
 	// Create webauthnCredential table
 	type webauthnCredential struct {
 		ID           int64  `xorm:"pk autoincr"`
-		CredentialID string `xorm:"INDEX"`
+		CredentialID string `xorm:"INDEX VARCHAR(410)"`
 	}
 	if err := x.Sync2(&webauthnCredential{}); err != nil {
 		return err