Testing: Remove quotes in COVERAGE

[marshallward]

The COVERAGE variable was incorrectly quoted, and was causing incorrect
quotes in the compile flag arguments.

This patch removes the redundant quotes.

[codecov-commenter]

Codecov Report

Merging #1212 into dev/gfdl will decrease coverage by 0.01%.
The diff coverage is 35.15%.

@@             Coverage Diff              @@
##           dev/gfdl    #1212      +/-   ##
============================================
- Coverage     46.08%   46.07%   -0.02%     
============================================
  Files           214      224      +10     
  Lines         69399    70592    +1193     
============================================
+ Hits          31984    32522     +538     
- Misses        37415    38070     +655     

Impacted Files	Coverage Δ
...g_src/external/GFDL_ocean_BGC/FMS_coupler_util.F90	0.00% <0.00%> (ø)
...fig_src/external/GFDL_ocean_BGC/generic_tracer.F90	0.00% <0.00%> (ø)
...c/external/GFDL_ocean_BGC/generic_tracer_utils.F90	0.00% <0.00%> (ø)
config_src/external/ODA_hooks/kdtree.f90	0.00% <0.00%> (ø)
config_src/external/ODA_hooks/ocean_da_core.F90	0.00% <0.00%> (ø)
config_src/external/ODA_hooks/ocean_da_types.F90	0.00% <0.00%> (ø)
config_src/external/ODA_hooks/write_ocean_obs.F90	0.00% <0.00%> (ø)
config_src/solo_driver/MESO_surface_forcing.F90	0.00% <0.00%> (ø)
config_src/solo_driver/user_surface_forcing.F90	0.00% <0.00%> (ø)
src/ALE/MOM_regridding.F90	31.47% <0.00%> (-0.17%)	⬇️
... and 213 more

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