config: make the config source const

The `struct git_config_source` passed to `config_with_options()` is
never modified. Let's mark it as `const` to clarify.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

config.c

@@ -125,7 +125,7 @@ struct config_include_data {
 	config_fn_t fn;
 	void *data;
 	const struct config_options *opts;
-	struct git_config_source *config_source;
+	const struct git_config_source *config_source;
 	struct repository *repo;
 
 	/*
@@ -2105,7 +2105,7 @@ static int do_git_config_sequence(const struct config_options *opts,
 }
 
 int config_with_options(config_fn_t fn, void *data,
-			struct git_config_source *config_source,
+			const struct git_config_source *config_source,
 			struct repository *repo,
 			const struct config_options *opts)
 {

config.h

@@ -232,7 +232,7 @@ void git_config(config_fn_t fn, void *);
  * sets `opts.respect_includes` to `1` by default.
  */
 int config_with_options(config_fn_t fn, void *,
-			struct git_config_source *config_source,
+			const struct git_config_source *config_source,
 			struct repository *repo,
 			const struct config_options *opts);