Fix C lint errors

[stdlib-bot]

C Linting Failures

Linting failures were detected in the automated lint workflow run.

Workflow Details

• Run: https://github.com/stdlib-js/stdlib/actions/runs/28724190257
• Type: C Linting
• Date: 2026-07-05 00:55:02 UTC

Error Details

lib/node_modules/@stdlib/number/float64/base/signbit/examples/c/example.c:25:9: style: Variable 'x' can be declared as const array [constVariable]
 double x[] = { 3.14, -3.14, 0.0, -0.0, 4.0, 1.0, -1.0, 1.0e308, -1.0e308 };
        ^

Pull Request Instructions

• Please use the following PR title format:
  "chore: fix C lint errors (issue #<ISSUE_NUMBER>)".
• Reference this issue in the "Related Issues" section of the PR body as "resolves #<ISSUE_NUMBER>".