sql: fix TestAuthenticationAndHBARules stress tests SSL issue

informs cockroachdb#131532
informs cockroachdb#131110
informs cockroachdb#130253
informs cockroachdb#127745
Epic CRDB-41958

TestAuthenticationAndHBARules fails for `special_cases`,
`hba_default_equivalence`, `empty_hba` data driven tests for secure mode. The
failures occur when root user is trying to authenticate with cert-password auth
method and `sslmode` is set to `verify-ca` with `sslcert` being empty. The
expected behavior is root authentication defaults to password method and fails
as no password is set for root, but instead we get:
```
SSL is not enabled on the server
```
Since the failures are there only under stress, it might be because db server
shutdown or paused before responding to request for upgrade connection to SSL
from lib/pq client from here
https://github.com/lib/pq/blob/3d613208bca2e74f2a20e04126ed30bcb5c4cc27/conn.go#L1116-L1130.
Retrying connection establishment when this specific error is obtained might fix
the problem as this logic seems faulty(it checks for absence of 'S' in server
response whereas the correct check should be for 'N' in response).

Release note: None

pkg/sql/pgwire/auth_test.go

@@ -572,7 +572,17 @@ func hbaRunTest(t *testing.T, insecure bool) {
 						defer dbSQL.Close()
 					}
 					if err != nil {
-						return "", err
+						if !errors.Is(err, pq.ErrSSLNotSupported) {
+							return "", err
+						}
+						// Retry: server might fail to respond for upgrade conn under stress
+						dbSQL, err = gosql.Open("postgres", dsn)
+						if dbSQL != nil {
+							defer dbSQL.Close()
+						}
+						if err != nil {
+							return "", err
+						}
 					}
 					row := dbSQL.QueryRow("SELECT current_catalog")
 					var result string