rust: Don't propagate apex across customBindgenTag

customBindgenTag is used to describe a particular host tool - don't
propagate apex dependency across it.

Bug: 249849807
Test: Adding rusqlite to apex no longer requires bindgen allowed
Change-Id: Ifcb2a94c577c72558f757bf10e975212558fe790
diff --git a/rust/rust.go b/rust/rust.go
index 1517e62..7342a14 100644
--- a/rust/rust.go
+++ b/rust/rust.go
@@ -1615,7 +1615,7 @@
 		}
 	}
 
-	if depTag == procMacroDepTag {
+	if depTag == procMacroDepTag || depTag == customBindgenDepTag {
 		return false
 	}