state-res: Fix default invite power level

According to matrix-org/matrix-spec#1021

crates/ruma-state-res/CHANGELOG.md

@@ -1,5 +1,11 @@
 # [unreleased]
 
+Bug fixes:
+
+* Change default `invite` power level to `0`
+  * The spec was determined to be wrong about the default:
+    <https://github.com/matrix-org/matrix-spec/pull/1021>
+
 Improvements:
 
 * Add `m.federate` to `auth_check`:

crates/ruma-state-res/src/event_auth.rs

@@ -361,7 +361,7 @@ pub fn auth_check<E: Event>(
             Some(power_levels) => {
                 from_json_str::<PowerLevelsContentInvite>(power_levels.content().get())?.invite
             }
-            None => int!(50),
+            None => int!(0),
         };
 
         if sender_power_level < invite_level {
@@ -502,7 +502,7 @@ fn valid_membership_change(
             // TODO Refactor all powerlevel parsing
             let invite = match from_json_str::<PowerLevelsContentInvite>(pl.content().get()) {
                 Ok(power_levels) => power_levels.invite,
-                _ => int!(50),
+                _ => int!(0),
             };
 
             if let Ok(content) = from_json_str::<PowerLevelsContentFields>(pl.content().get()) {