Update test-runners.md to fix grammar errors

[bwanamaina]

fixed grammar errors

[codecov[bot]]

Codecov Report

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

Comparison is base (c8f628f) 91.31% compared to head (78235a2) 91.31%. Report is 1 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #830 +/- ## ======================================= Coverage 91.31% 91.31% ======================================= Files 15 15 Lines 1981 1981 Branches 499 499 ======================================= Hits 1809 1809 Misses 163 163 Partials 9 9 ```

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:tada: This PR is included in version 9.1.2 :tada:

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