Single-core tasks shouldn't request more than 1 core

[muffato]

Follow-up of #1630 . For single-core tasks, there is no need to increase the number of cores at each attempt

PR checklist

• This comment contains a description of changes (with reason)
• CHANGELOG.md is updated
• If you've fixed a bug or added code that should be tested, add tests!
• Documentation in docs is updated

[codecov]

Codecov Report

Merging #1678 (0fd5cdc) into dev (d5ee441) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##              dev    #1678   +/-   ##
=======================================
  Coverage   68.00%   68.00%           
=======================================
  Files          56       56           
  Lines        6589     6589           
=======================================
  Hits         4481     4481           
  Misses       2108     2108           

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[matthdsm]

Looks good and makes more sense than it did previously!

[JoseEspinosa]

LGTM

[matthdsm]

Thanks!

[muffato]

Thanks all