Merge pull request #3644 from vkarak/bugfix/default-perflog-datefmt

[bugfix] Fix default `datefmt` for the perflog handlers

Author: vkarak

reframe/schemas/config.json

@@ -650,7 +650,7 @@
         "logging/handlers*/syslog_socktype": "udp",
         "logging/handlers*/syslog_facility": "user",
         "logging/handlers/*_datefmt": "%FT%T.%f",
-        "logging/handlers_perflog/datefmt": "%FT%T",
+        "logging/handlers_perflog/*_datefmt": "%FT%T",
         "logging/handlers_perflog/filelog_append": true,
         "logging/handlers_perflog/filelog_basedir": "./perflogs",
         "logging/handlers_perflog/filelog_ignore_keys": [],