Fix coveralls reporting from github actions

[djhoese]

Coveralls keeps reporting 0. It may be that it expects a certain file format to be generated. This PR is me figuring it out.

[codecov]

Codecov Report

Merging #328 (e481db3) into master (23e78a6) will decrease coverage by 1.44%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #328      +/-   ##
==========================================
- Coverage   92.74%   91.29%   -1.45%     
==========================================
  Files          44       45       +1     
  Lines        9226     9505     +279     
==========================================
+ Hits         8557     8678     +121     
- Misses        669      827     +158     

Flag	Coverage Δ
unittests	91.29% <ø> (-1.45%)	⬇️

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Impacted Files	Coverage Δ
pyresample/version.py	43.36% <0.00%> (ø)

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[coveralls]

Coverage increased (+91.2%) to 91.239% when pulling a6e2a07 on djhoese:ci-cov-fix into 23e78a6 on pytroll:master.