test: update mssql envvar to MSSQL_SA_PASSWORD

[trentm]

Per https://learn.microsoft.com/en-us/sql/linux/sql-server-linux-configure-environment-variables
SA_PASSWORD (without the prefix) is deprecated.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.75%. Comparing base (dfb2dff) to head (0b55513).
Report is 244 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2447      +/-   ##
==========================================
- Coverage   90.97%   90.75%   -0.23%     
==========================================
  Files         146      156      +10     
  Lines        7492     7700     +208     
  Branches     1502     1583      +81     
==========================================
+ Hits         6816     6988     +172     
- Misses        676      712      +36     

see 76 files with indirect coverage changes