sql: Drop Role does not properly check if target user does not exist

[Dedej-Bergin]

Describe the problem

If we set the role as admin and we try to drop a user that does not exist, we give the impression that the command succeeded instead of properly erroring out.

To Reproduce

CREATE ROLE IF NOT EXISTS migrator;
CREATE USER goose_catalogs WITH PASSWORD '123';
CREATE DATABASE catalogs_staging;
USE catalogs_staging; 
ALTER DEFAULT PRIVILEGES FOR ALL ROLES GRANT CREATE, DROP, SELECT, INSERT, UPDATE, DELETE ON tables TO migrator;
GRANT CREATE, DROP, SELECT, INSERT, UPDATE, DELETE ON ALL TABLES IN SCHEMA catalogs_staging.public TO migrator;
GRANT CREATE ON SCHEMA catalogs_staging.public TO migrator;
GRANT migrator TO goose_catalogs WITH ADMIN OPTION;
GRANT SYSTEM CONTROLJOB, CREATEROLE, CREATELOGIN TO goose_catalogs;
show users;


SET ROLE goose_catalogs;
SHOW ROLE;
DROP USER IF EXISTS goose_catalogs_staging_202410212225;
-- we get the proper error that we should get


SET ROLE admin;
SHOW ROLE;
DROP USER IF EXISTS goose_catalogs_staging_202410212225;
-- no error and it looks like the drop succeeded

Environment:
CockroachDB Version: v24.1.6

Additional context
Was first hit by this customer here: https://github.com/cockroachlabs/support/issues/3118

Jira issue: CRDB-44125

Epic CRDB-43310

[blathers-crl]

Hi @Dedej-Bergin, please add branch-* labels to identify which branch(es) this C-bug affects.

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}

[blathers-crl]

Based on the specified backports for linked PR #134850, I applied the following new label(s) to this issue: branch-release-23.2, branch-release-24.1, branch-release-24.2, branch-release-24.3. Please adjust the labels as needed to match the branches actually affected by this issue, including adding any known older branches.

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}