enable valgrind for AStar

cli/tests/cli_run.rs

@@ -236,7 +236,7 @@ mod cli_run {
             "astar-tests",
             &[],
             "True\n",
-            false,
+            true,
         );
     }
 

compiler/builtins/bitcode/src/dict.zig

@@ -672,6 +672,7 @@ pub fn dictUnion(dict1: RocDict, dict2: RocDict, alignment: Alignment, key_width
                         inc_key(key);
                         inc_value(value);
 
+                        // we know the newly added key is not a duplicate, so the `dec`s are unreachable
                         const dec_key = doNothing;
                         const dec_value = doNothing;