Fix stack overflow in tests

Just calling parseAssignExpression instead of parseExpression in AA
checking now, since that's what's being done in the parsing code
anyway!

src/dparse/parser.d

@@ -8400,7 +8400,7 @@ protected: final:
         immutable b = setBookmark();
         scope(exit) goToBookmark(b);
         advance();
-        immutable bool result = !currentIs(tok!"]") && parseExpression() !is null && currentIs(tok!":");
+        immutable bool result = !currentIs(tok!"]") && parseAssignExpression() !is null && currentIs(tok!":");
         cachedAAChecks[currentIndex] = result;
         return result;
     }