bug#69405: [PATCH] .emacs.d/tree-sitter/ not used in tree-sitter tests

[Eli Zaretskii]

> Cc: Yuan Fu <casouri@gmail.com>
> From: Mattias Engdegård <mattias.engdegard@gmail.com>
> Date: Mon, 26 Feb 2024 14:36:39 +0100
> 
> The .emacs.d/tree-sitter/ directory isn't searched when running tests 
> non-interactively. The Makefile sets HOME to /nonexistent, which is correct 
> but has the unfortunate side-effect of not running all the tests properly 
> even with the compiled grammars installed.
> 
> The attached patch adds an environment variable, EMACS_TREE_SITTER_DIR, and 
> sets it in the Makefile. I didn't bother documenting it because it's only 
> intended for use in our own tests.

Can't we do that in the test harness, instead of introducing
test-suite dependencies into the built Emacs binary?  For example, how
about adding to tree-sitter-extra-load-path in treesit-tests.el
instead?

Thanks.