Upgrade setup-go action version in README

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 70.50%. Comparing base (14707cd) to head (75e8b6e). Report is 4 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #455 +/- ## ========================================== + Coverage 66.92% 70.50% +3.58% ========================================== Files 3 3 Lines 130 139 +9 Branches 23 32 +9 ========================================== + Hits 87 98 +11 - Misses 27 37 +10 + Partials 16 4 -12 ```

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[caarlos0]

thank you!