[code-quality] Apply ruff linting suggestions (#7206)

esphome/config_validation.py

@@ -91,7 +91,7 @@ _LOGGER = logging.getLogger(__name__)
 
 # pylint: disable=consider-using-f-string
 VARIABLE_PROG = re.compile(
-    "\\$([{0}]+|\\{{[{0}]*\\}})".format(VALID_SUBSTITUTIONS_CHARACTERS)
+    f"\\$([{VALID_SUBSTITUTIONS_CHARACTERS}]+|\\{{[{VALID_SUBSTITUTIONS_CHARACTERS}]*\\}})"
 )
 
 # pylint: disable=invalid-name

esphome/mqtt.py

@@ -3,7 +3,6 @@ import hashlib
 import json
 import logging
 import ssl
-import sys
 import time
 
 import paho.mqtt.client as mqtt
@@ -103,10 +102,7 @@ def prepare(
     if config[CONF_MQTT].get(CONF_SSL_FINGERPRINTS) or config[CONF_MQTT].get(
         CONF_CERTIFICATE_AUTHORITY
     ):
-        if sys.version_info >= (2, 7, 13):
         tls_version = ssl.PROTOCOL_TLS  # pylint: disable=no-member
-        else:
-            tls_version = ssl.PROTOCOL_SSLv23
         client.tls_set(
             ca_certs=None,
             certfile=None,