Fix some ruff error

```
ruff now_lms
now_lms\vistas\web_error_codes.py:32:30: F401 [*] `flask.flash` imported but unused
now_lms\vistas\web_error_codes.py:32:37: F401 [*] `flask.redirect` imported but unused
now_lms\vistas\web_error_codes.py:32:64: F401 [*] `flask.request` imported but unused
now_lms\vistas\web_error_codes.py:33:25: F401 [*] `flask_login.login_required` imported but unused
now_lms\vistas\web_error_codes.py:34:28: F401 [*] `sqlalchemy.exc.OperationalError` imported but unused
now_lms\vistas\web_error_codes.py:39:26: F401 [*] `now_lms.auth.perfil_requerido` imported but unused
now_lms\vistas\web_error_codes.py:41:24: F401 [*] `now_lms.db.MAXIMO_RESULTADOS_EN_CONSULTA_PAGINADA` imported but unused
now_lms\vistas\web_error_codes.py:41:64: F401 [*] `now_lms.db.Etiqueta` imported but unused
now_lms\vistas\web_error_codes.py:41:74: F401 [*] `now_lms.db.database` imported but unused
now_lms\vistas\web_error_codes.py:42:30: F401 [*] `now_lms.db.tools.cursos_por_etiqueta` imported but unused
now_lms\vistas\web_error_codes.py:43:27: F401 [*] `now_lms.forms.EtiquetaForm` imported but unused
```

Signed-off-by: William José Moreno Reyes <williamjmorenor@gmail.com>

Author: williamjmorenor

now_lms/vistas/web_error_codes.py

@@ -29,18 +29,12 @@
 # ---------------------------------------------------------------------------------------
 # Librerias de terceros
 # ---------------------------------------------------------------------------------------
-from flask import Blueprint, flash, redirect, render_template, request
-from flask_login import login_required
-from sqlalchemy.exc import OperationalError
+from flask import Blueprint, render_template
 
 # ---------------------------------------------------------------------------------------
 # Recursos locales
 # ---------------------------------------------------------------------------------------
-from now_lms.auth import perfil_requerido
 from now_lms.config import DIRECTORIO_PLANTILLAS
-from now_lms.db import MAXIMO_RESULTADOS_EN_CONSULTA_PAGINADA, Etiqueta, database
-from now_lms.db.tools import cursos_por_etiqueta
-from now_lms.forms import EtiquetaForm
 
 # ---------------------------------------------------------------------------------------
 # Administración de Etiquetas.