ci(release): avoid heredoc in workflow guard

[crup]

Fixes the release workflow YAML parser error reported on line 109 by replacing the embedded heredoc with a node -e command inside the guard step.

Context:

• PR ci(release): refine stable release workflow #4 moved docs/install guidance to npm latest and added stable-release dropdown inputs.
• GitHub rejected release.yml because the heredoc terminator inside the YAML block was parsed as invalid YAML.

Validation run locally:

• pnpm readme:check
• git diff --check

[github-actions]

Bundle size report

Entry	Files	Raw	Gzip	Brotli	Raw delta	Gzip delta	Brotli delta
core	2	4.44 kB	1.52 kB	1.40 kB	0 B	0 B	0 B
timer group add-on	3	10.93 kB	3.83 kB	3.50 kB	0 B	0 B	0 B
schedules add-on	3	8.62 kB	3.02 kB	2.78 kB	0 B	0 B	0 B
duration helper	1	318 B	224 B	192 B	0 B	0 B	0 B
diagnostics helper	1	105 B	115 B	90 B	0 B	0 B	0 B
core CJS	1	4.71 kB	1.63 kB	1.50 kB	0 B	0 B	0 B
timer group CJS	1	11.02 kB	3.86 kB	3.54 kB	0 B	0 B	0 B
schedules CJS	1	8.71 kB	3.04 kB	2.81 kB	0 B	0 B	0 B
duration CJS	1	808 B	475 B	424 B	0 B	0 B	0 B
diagnostics CJS	1	605 B	367 B	326 B	0 B	0 B	0 B