chore: remove redundant parentheses flagged by gofumpt

golangci-lint v2.13.0 ships a gofumpt that strips parentheses around a
single expression. lint.yml asks for `version: latest`, so CI picked it up
and every lint job went red on code untouched since 2014.

No behaviour change. Applied with `golangci-lint fmt` over every
GOOS/GOARCH in the lint matrix, so the build-tagged files under disk/ are
covered too, not just the three the linux job reported.