test(coderd/x/chatd): skip TestExploreChatSendMessageCannotMutateMCPSnapshot (#25023)

Skips `TestExploreChatSendMessageCannotMutateMCPSnapshot` while the
chatd redesign is in flight. The test exposes a self-interrupt race in
`processChat`'s control-pubsub subscriber that is structurally fixed by
the redesign in #24444; skipping until then matches the existing
`TestSubscribeRelayEstablishedMidStream` skip in
`enterprise/coderd/x/chatd/chatd_test.go`.

Relates to https://github.com/coder/internal/issues/1493.

coderd/x/chatd/chatd_test.go

@@ -1092,6 +1092,8 @@ func TestRootExploreChatExcludesWebSearchProviderToolAtRuntime(t *testing.T) {
 
 func TestExploreChatSendMessageCannotMutateMCPSnapshot(t *testing.T) {
 	t.Parallel()
+	// TODO(hugodutka): Unskip when chatd is free of race conditions.
+	t.Skip("skipped due to inherent race condition; see https://github.com/coder/internal/issues/1493")
 
 	db, ps := dbtestutil.NewDB(t)
 	ctx := testutil.Context(t, testutil.WaitLong)