Fix cross-database data source confusion

[natehuangting]

For #19894

[codecov-commenter]

Codecov Report

Merging #19939 (4befc5d) into master (dfbdd38) will decrease coverage by 0.00%.
The diff coverage is 57.14%.

@@             Coverage Diff              @@
##             master   #19939      +/-   ##
============================================
- Coverage     60.21%   60.20%   -0.01%     
  Complexity     2424     2424              
============================================
  Files          3878     3878              
  Lines         54991    54991              
  Branches       7693     7693              
============================================
- Hits          33111    33108       -3     
- Misses        19037    19040       +3     
  Partials       2843     2843              

Impacted Files	Coverage Δ
...nd/communication/vertx/VertxBackendConnection.java	0.00% <0.00%> (ø)
...ication/jdbc/connection/JDBCBackendConnection.java	82.99% <100.00%> (ø)
...handler/distsql/ral/hint/enums/HintSourceType.java	0.00% <0.00%> (-42.86%)	⬇️

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