math: Print special error for logical operators

Until now, something like

`math '7 = 2'`

would complain about a "missing" operator.

Now we print an error about logical operators not being supported and
point the user towards `test`.

Fixes #6096

src/tinyexpr.cpp

@@ -306,6 +306,15 @@ void next_token(state *s) {
                     case '\n':
                     case '\r':
                         break;
+                    case '=':
+                    case '>':
+                    case '<':
+                    case '&':
+                    case '|':
+                    case '!':
+                        s->type = TOK_ERROR;
+                        s->error = TE_ERROR_LOGICAL_OPERATOR;
+                        break;
                     default:
                         s->type = TOK_ERROR;
                         s->error = TE_ERROR_MISSING_OPERATOR;