Fix exporting values into Postgres

[gzsombor]

Fixing go-gitea/gitea#5651

• UUID and BOOL type shouldn't have a length field
• Incorrect quoting cause that the column names are selected instead of the column values

[codecov-io]

Codecov Report

Merging #1186 into master will increase coverage by <.01%.
The diff coverage is 50%.

@@            Coverage Diff             @@
##           master    #1186      +/-   ##
==========================================
+ Coverage   54.69%   54.69%   +<.01%     
==========================================
  Files          42       42              
  Lines        7646     7649       +3     
==========================================
+ Hits         4182     4184       +2     
- Misses       2935     2936       +1     
  Partials      529      529

Impacted Files	Coverage Δ
engine.go	61.52% <0%> (-0.07%)	⬇️
dialect_postgres.go	75.72% <100%> (+0.15%)	⬆️

---

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[codecov-io]

Codecov Report

Merging #1186 into master will increase coverage by <.01%.
The diff coverage is 50%.

@@            Coverage Diff             @@
##           master    #1186      +/-   ##
==========================================
+ Coverage   54.69%   54.69%   +<.01%     
==========================================
  Files          42       42              
  Lines        7646     7649       +3     
==========================================
+ Hits         4182     4184       +2     
- Misses       2935     2936       +1     
  Partials      529      529

Impacted Files	Coverage Δ
engine.go	61.52% <0%> (-0.07%)	⬇️
dialect_postgres.go	75.72% <100%> (+0.15%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update a8f0a71...b255dcb. Read the comment docs.