Constify some arguments
Even GCC complains, given how it's used (assuming `-Wwrite-strings`):
../../../src/tagmanager/tm_parser.c: In function 'tm_parser_update_scope':
../../../src/tagmanager/tm_parser.c:1469:65: warning: passing argument 2 of 'replace_string_if_present' discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]
1469 | return replace_string_if_present(scope, "\\", "::");
| ^~~~
../../../src/tagmanager/tm_parser.c:1447:66: note: expected 'gchar *' {aka 'char *'} but argument is of type 'const char *'
1447 | static gchar *replace_string_if_present(gchar *haystack, gchar *needle, gchar *subst)
| ~~~~~~~^~~~~~
../../../src/tagmanager/tm_parser.c:1469:71: warning: passing argument 3 of 'replace_string_if_present' discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]
1469 | return replace_string_if_present(scope, "\\", "::");
| ^~~~
../../../src/tagmanager/tm_parser.c:1447:82: note: expected 'gchar *' {aka 'char *'} but argument is of type 'const char *'
1447 | static gchar *replace_string_if_present(gchar *haystack, gchar *needle, gchar *subst)
| ~~~~~~~^~~~~