Drop -c short flag from --config-file to fix duplicate parameter warning

[MGpromax]

Fixes #5265

As suspected in the issue, commit 1c04c47 (the new --config-file option) is the culprit: it declared -c as its short flag, which collides with the long-standing -c/--copyright option from the copyright scanner plugin (src/cluecode/plugin_copyright.py). click then emits the UserWarning: The parameter -c is used more than once on every invocation.

Fix: drop the -c short flag from --config-file, keeping -c for --copyright as documented everywhere. Since --config-file has not shipped in any release yet (no tag contains 1c04c47), this is not a breaking change for released users.

Also updated:

• tests/scancode/data/help/help.txt regenerated with SCANCODE_REGEN_TEST_FIXTURES (the whole core: group re-flows because that row set the option column width); the same regenerated core: block applied to help_linux.txt
• the two docs pages that embed the help row (docs/source/rst-snippets/cli-core-options.rst, docs/source/reference/scancode-cli/cli-help-text-options.rst)

Validation:

• scancode -c --json-pp out.json <file> no longer emits the warning and the copyright scan works
• pytest tests/scancode/test_cli.py tests/scancode/test_ignore.py passes locally (including the --config-file tests added with the original commit)

Tasks

• Reviewed contribution guidelines
• PR is descriptively titled 📑 and links the original issue above 🔗
• Tests pass -- look for a green checkbox ✔️ a few minutes after opening your PR
• Commits are in uniquely-named feature branch and has no merge conflicts 📁
• Updated documentation pages (if applicable)
• Updated CHANGELOG.rst (if applicable) -- not applicable, the option is unreleased