pgood_wait: fix bool include

We don't actually have a CI build type for plain Make anymore, so we
don't get any repository level CI done for this repository.  The
Yocto recipe update failed with the following:

```
15:12:53 | pgood_wait.c:95:16: error: 'true' undeclared (first use in this function)
```

Make a simple fix to add `stdbool.h` in hopes that this solves it.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I64dd3cba36c7b9b3aa8111ffe6f7fb33088eb080
diff --git a/op-pwrctl/pgood_wait/pgood_wait.c b/op-pwrctl/pgood_wait/pgood_wait.c
index e7ddb8c..069ee35 100644
--- a/op-pwrctl/pgood_wait/pgood_wait.c
+++ b/op-pwrctl/pgood_wait/pgood_wait.c
@@ -13,8 +13,9 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-#include <stdlib.h>
+#include <stdbool.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <errno.h>
 #include <systemd/sd-bus.h>
 #include <systemd/sd-event.h>