[ci] Link check job is broken

[StrikerRUS]

https://github.com/microsoft/LightGBM/actions/workflows/linkchecker.yml

Error: Config file .linkcheckerrc does not exist.
Execute '/home/runner/miniforge/envs/test-env/bin/linkchecker -h' for help

https://github.com/microsoft/LightGBM/actions/runs/12328181037/job/34411048698#step:3:3749

Job and config file:

LightGBM/.github/workflows/linkchecker.yml

Line 14 in b33a12e

TASK: 'check-links'

LightGBM/.ci/test.sh

Lines 147 to 152 in b33a12e

	if [[ $TASK == "check-links" ]]; then
	# check docs for broken links
	pip install linkchecker
	linkchecker --config=.linkcheckerrc ./docs/_build/html/*.html || exit 1
	exit 0
	fi

LightGBM/docs/.linkcheckerrc

Line 1 in b33a12e

[checking]

[jameslamb]

Oh wow, thank you for finding this! I haven't checked that job in a while.

Suspect that I accidentally broke this somewhere around #6497. I'll put up a PR to fix it.