Gridspec in virtual product tests

[SpacemanPaul]

Reason for this pull request

Virtual Product tests were throwing a deprecation warning because they use the old datacube GridSpec. Also that deprecation warning had a spelling mistake,

Proposed changes

• Correct the spelling of the GridSpec deprecation warning.

• Get virtual products tests using the odc-geo GridSpec class.

• Tests added / passed

• Fully documented, including docs/about/whats_new.rst for all changes

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (e74a27b) 85.22% compared to head (95a08a4) 85.19%.

Additional details and impacted files

@@               Coverage Diff               @@
##           develop-1.9    #1512      +/-   ##
===============================================
- Coverage        85.22%   85.19%   -0.04%     
===============================================
  Files              131      131              
  Lines            14551    14551              
===============================================
- Hits             12401    12396       -5     
- Misses            2150     2155       +5     

Files	Coverage Δ
datacube/model/__init__.py	95.14% <ø> (-0.38%)	⬇️

... and 1 file with indirect coverage changes

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