Strengthen MSSQL QueryBuilderTest and SchemaTest coverage

[WarLikeLaux]

Q	A
Is bugfix?	❌
New feature?	❌
Tests added?	✔️
Breaks BC?	❌
Fixed issues

What does this PR do?

Adds tests for previously uncovered methods in MSSQL QueryBuilder, Schema and InConditionBuilder.

Coverage

File	Before	After
mssql/QueryBuilder.php	80.4% (185/230)	95.7% (220/230)
mssql/Schema.php	80.8% (231/286)	92.7% (265/286)

New test methods: 13 in QueryBuilderTest, 11 in SchemaTest.

Remaining uncovered: pre-2012/pre-2017 SQL Server branches, cross-catalog paths, dead code (getAllColumnNames, isOldMssql).

Changelog not required, because no source files changed.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.38%. Comparing base (37b6e7b) to head (1624982).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #20795      +/-   ##
============================================
+ Coverage     80.13%   80.38%   +0.24%     
  Complexity    11533    11533              
============================================
  Files           374      374              
  Lines         30206    30206              
============================================
+ Hits          24207    24281      +74     
+ Misses         5999     5925      -74     

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