deps: update dependency org.checkerframework:checker-qual to v3.21.1 (googleapis#554)

Author: renovate-bot

Diff for: third-party-dependencies/pom.xml

@@ -69,7 +69,7 @@
     <httpcomponents.httpcore.version>4.4.15</httpcomponents.httpcore.version>
     <httpcomponents.httpclient.version>4.5.13</httpcomponents.httpclient.version>
     <!-- ensure checker-qual version matches what Guava uses -->
-    <checker-qual.version>3.20.0</checker-qual.version>
+    <checker-qual.version>3.21.1</checker-qual.version>
   </properties>
 
   <dependencyManagement>