Unclear reference threshold log attribute names

[mahendrapaipuri]

Before ReFrame 4.0.0, the placeholders for upper and lower reference threshold values are check_perf_{upper,lower}_thres for formatting performance logs. Using the same in ReFrame 4.0.1 spits KeyError during performance logging as follows:

Traceback (most recent call last):
  File "[redacted]/reframe/lib/python3.10/logging/__init__.py", line 1100, in emit
    msg = self.format(record)
  File "[redacted]/reframe/lib/python3.10/logging/__init__.py", line 943, in format
    return fmt.format(record)
  File "[redacted]/reframe/lib/python3.10/logging/__init__.py", line 681, in format
    s = self.formatMessage(record)
  File "[redacted]/reframe/reframe/core/logging.py", line 301, in formatMessage
    record_proxy[k] = self._format_perf(v)
  File "[redacted]reframe/reframe/core/logging.py", line 286, in _format_perf
    chunks.append(self.__fmtperf % record)
KeyError: 'check_perf_lower_thres'

If we remove the suffix _thres, ie, using check_perf_{upper,lower} the error goes away and performance logging works normally. Even in the docs, the attribute names are unclear.