`long` is a future-reserved word the Qt 6.7 QML parser on the CI runner still
rejects, while newer local Qt builds accept it as an ordinary identifier. A
local named `long` compiled here and failed there, which is the second time
this repo has paid for it: 506efa0 renamed the same word in the normalizer
tests and left nothing behind to catch the next one.

Rename the local in tst_cost_presentation.qml, and add the guard that should
have come with the first fix. qmllint cannot help, because the file never
reaches it once the parser gives up, so the check greps the `all` surface and
tests/ for the reserved words used after var, let, or const.

Verified by reintroducing `var long`: the check exits 1 and names the file and
line, and `make check` exits 2. Without it, both stayed green locally and only
CI caught the parse failure.