Trying to return integer sometimes to match SQLite led to more problems
that I anticipated. The reason being, we can't *really* match SQLite's
behavior unless we know the type of *every* element in the sum. This is
not impossible, but it is very hard, for very little gain.
Fixes#3831
When adding tests for extensions, please follow these guidelines:
Tests that verify the internal logic or behavior of a particular extension should go into cli_tests/extensions.py.
Tests that verify how extensions interact with the database engine, such as virtual table handling, should be written
in TCL (see vtab.test as an example).
To check which extensions are available in TCL, or to add a new one, refer to the tester.tcl file and look at the extension_map.
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