Fix average_precision metric

[elias-ramzi]

What does this PR do?

This PR fixes pytorch_lightning.metrics.functional.average_precision. It also adds a test that would have failed with the old implementation

Parentheses were missing in the definition of the function.

Bug described in #2315.

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PR review

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[codecov]

Codecov Report

Merging #2319 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #2319   +/-   ##
======================================
  Coverage      88%     88%           
======================================
  Files          70      70           
  Lines        5501    5501           
======================================
  Hits         4834    4834           
  Misses        667     667           

[elias-ramzi]

Hi !
Could you help me on the CI checks. I don't understand why some checks are failing, and I don't understand the logs that are produced 😕

[Borda]

Could you help me on the CI checks. I don't understand why some checks are failing, and I don't understand the logs that are produced

it was not related to your code, just random GitHub issue 🐰

[elias-ramzi]

Ok thank you, I thought so but wasn't sure! ☺️

[SkafteNicki]

LGTM