[tests] fix spelling errors (#11640)

tests/gtest/fake_platform.cpp

@@ -164,7 +164,7 @@ void FakePlatform::ProcessSchedules(uint64_t &aTimeout)
 
     if (alarm == &guard)
     {
-        // nonthing scheduled within this period.
+        // nothing scheduled within this period.
     }
     else if (alarm == &mReceiveAtEnd)
     {

tests/scripts/thread-cert/backbone/test_mlr_multicast_routing_timeout.py

@@ -165,7 +165,7 @@ class TestMlrTimeout(thread_cert.TestCase):
         # PBBR should forward this ping request to Thread network because MA doesn't expire yet
         pkts.filter_wpan_src64(PBBR).filter_AMPLFMA().filter_ping_request(
             identifier=ping.icmpv6.echo.identifier).must_next()
-        # Router should NOT reply because it has unsubcribed the multicast address
+        # Router should NOT reply because it has unsubscribed the multicast address
         pkts.filter_wpan_src64(ROUTER).filter_ipv6_dst(HOST_BGUA).filter_ping_reply(
             identifier=ping.icmpv6.echo.identifier).must_not_next()
 

tests/unit/test_mdns.cpp

@@ -4525,7 +4525,7 @@ void TestQuery(void)
     VerifyOrQuit(dnsMsg != nullptr);
     VerifyOrQuit(dnsMsg->GetNext() == nullptr);
 
-    // Response should include `service3` only since anwer TTL
+    // Response should include `service3` only since answer TTL
     // is less than half of registered TTL
 
     dnsMsg->ValidateHeader(kMulticastResponse, /* Q */ 0, /* Ans */ 1, /* Auth */ 0, /* Addnl */ 4);