The Home Office does not hold the information requested.
The Home Office collects and publishes data on the number of police officers that have left the service through ‘medical retirement’ in the annual ‘Police workforce, England and Wales’ statistical bulletin:
However, data on how many of those medical retirements that are due to injury are not available from the data held centrally.
The Home Office collects data on the number of assaults on police officers and these are published quarterly by the Office for National Statistics. The latest figures, for the year ending March 2020, can be accessed on the ONS website (available here):
However, it not possible to identify the ethnicity of victims, nor is it possible to identify whether or not a weapon was used in the assault.