Change gendered terms to be gender-neutral (#21325)

Some typos are also fixed.

src/hostname/hostnamectl.c

@@ -442,7 +442,7 @@ static int set_hostname(int argc, char **argv, void *userdata) {
                  * dot if there is one. If it was not valid, then it will be made fully valid by truncating, dropping
                  * multiple dots, and dropping weird chars. Note that we clean the name up only if we also are
                  * supposed to set the pretty name. If the pretty name is not being set we assume the user knows what
-                 * he does and pass the name as-is. */
+                 * they are doing and pass the name as-is. */
                 h = strdup(hostname);
                 if (!h)
                         return log_oom();