make gsp_id column unique

[peterdudfield]

Pull Request

Description

Make gsp id columns in LocationSQL distinct

Fixes #44

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• [ ] Yes

If your changes affect data processing, have you plotted any changes? i.e. have you done a quick sanity check?

• [ ] Yes

Checklist:

• [x] My code follows OCF's coding style guidelines
• [x] I have performed a self-review of my own code
• [ ] I have made corresponding changes to the documentation
• [ ] I have added tests that prove my fix is effective or that my feature works
• [x] I have checked my code and corrected any misspellings

[codecov-commenter]

Codecov Report

Merging #45 (884954a) into main (04815bc) will increase coverage by 0.04%. The diff coverage is 95.65%.

@@            Coverage Diff             @@
##             main      #45      +/-   ##
==========================================
+ Coverage   98.33%   98.37%   +0.04%     
==========================================
  Files          16       16              
  Lines         602      617      +15     
==========================================
+ Hits          592      607      +15     
  Misses         10       10              

Impacted Files	Coverage Δ
nowcasting_datamodel/read/read.py	99.23% <90.00%> (+0.06%)	:arrow_up:
nowcasting_datamodel/__init__.py	100.00% <100.00%> (ø)
nowcasting_datamodel/fake.py	100.00% <100.00%> (ø)
nowcasting_datamodel/models/gsp.py	93.65% <100.00%> (+0.20%)	:arrow_up:
nowcasting_datamodel/national.py	92.10% <100.00%> (+0.67%)	:arrow_up:

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