[Failing Test] - `forecast_calibration_test.py` - Beijing o3

[mwalker-scottlogic]

Running the backend regression tests yesterday and this morning, I picked up a test failure in forecast_calibration_test.py.

The test compares the forecast data on the ftp server for a specific base time to the forecast data stored in the database for the same base time and checks there isn't a divergence of more than 3%.

The test failure is specifically for Beijing, and for the pollutant o3

[Ben-EJ]

It would seem that the number from the FTP has been rounded and because the numbers are so small this is causing a massive differential causing the error.

[mwalker-scottlogic]

PR raised to amend test to round to 3dp