SNOW-957736: Fix SnowflakeDbConnection.Dispose behaviour

[sfc-gh-pbulawa]

Description

The connection which is not closed properly by the user should not enter the connection pool.

Checklist

• Code compiles correctly
• Code is formatted according to Coding Conventions
• Created tests which fail without the change (if possible)
• All tests passing (dotnet test)
• Extended the README / documentation, if necessary
• Provide JIRA issue id (if possible) or GitHub issue id in PR name

[codecov]

Codecov Report

Merging #807 (e434e18) into master (7f73791) will increase coverage by 0.08%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #807      +/-   ##
==========================================
+ Coverage   83.54%   83.62%   +0.08%     
==========================================
  Files          89       89              
  Lines        9146     9155       +9     
  Branches      835      837       +2     
==========================================
+ Hits         7641     7656      +15     
+ Misses       1278     1272       -6     
  Partials      227      227              

Files	Coverage Δ
Snowflake.Data/Client/SnowflakeDbConnection.cs	84.88% <100.00%> (+0.54%)	⬆️

... and 1 file with indirect coverage changes

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