init: fix bug regarding ~/ expansion in init.templateDir

We used to read the init.templateDir setting at builtin/init-db.c using a git_config() callback that, in turn, called git_config_pathname(). To simplify the config reading logic at this file and plug a memory leak, this was replaced by a direct call to git_config_get_value() at e4de4502e6 ("init: remove git_init_db_config() while fixing leaks", 2021-03-14). However, this function doesn't provide path expanding semantics, like git_config_pathname() does, so paths with '~/' and '~user/' are treated literally. This makes 'git init' fail to handle init.templateDir paths using these constructs: $ git config init.templateDir '~/templates_dir' $ git init 'warning: templates not found in ~/templates_dir' Replace the git_config_get_value() call by git_config_get_pathname(), which does the '~/' and '~user/' expansions. Also add a regression test. Note that unlike git_config_get_value(), the config cache does not own the memory for the path returned by git_config_get_pathname(), so we must free() it. Reported on IRC by rkta. Signed-off-by: Matheus Tavares <matheus.bernardino@usp.br> Signed-off-by: Junio C Hamano <gitster@pobox.com>