Fix: handle float32 according to spec in all cases

[CL-Jeremy]

I encountered what looks quite similar to the issue submitter's case, so I replied in that issue and did a follow-up there: uptrace/bun#993 (comment).

According to the spec (https://pkg.go.dev/database/sql#Scanner), single-precision float values must always be returned as doubles, which could then be downcasted to recover the original value (leaving the binary representation unchanged, so there is no loss of precision if handled properly).

This bug is only present in readFixedType, so it seems to be due to carelessness.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 74.74%. Comparing base (9b84d9b) to head (72eb428).

Files	Patch %	Lines
types.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #208      +/-   ##
==========================================
- Coverage   74.79%   74.74%   -0.05%     
==========================================
  Files          32       32              
  Lines        6379     6379              
==========================================
- Hits         4771     4768       -3     
- Misses       1325     1327       +2     
- Partials      283      284       +1     

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[shueybubbles]

@CL-Jeremy if you want to finish the change, just include the test update as part of this same PR. No need for separate changes.