env-util: drop _pure_ for strv_env_get_n

This function calls getenv() internally, making it
non-pure, as envvars can change between two calls
even if passed arguments are the same.

src/basic/env-util.c

@@ -529,7 +529,7 @@ int _strv_env_assign_many(char ***l, ...) {
         return 0;
 }
 
-char* strv_env_get_n(char **l, const char *name, size_t k, ReplaceEnvFlags flags) {
+char* strv_env_get_n(char * const *l, const char *name, size_t k, ReplaceEnvFlags flags) {
         assert(name);
 
         if (k == SIZE_MAX)
@@ -539,7 +539,7 @@ char* strv_env_get_n(char **l, const char *name, size_t k, ReplaceEnvFlags flags
 
         STRV_FOREACH_BACKWARDS(i, l)
                 if (strneq(*i, name, k) && (*i)[k] == '=')
-                        return *i + k + 1;
+                        return (char*) *i + k + 1;
 
         if (flags & REPLACE_ENV_USE_ENVIRONMENT) {
                 const char *t;