docs: Fix broken RubyDoc URL fragments

Some RubyDoc URL fragments in the Formula Cookbook documentation
include an equals sign (`%3D`) but the `id` attributes in the current
RubyDoc HTML don't include the equals sign, so the documentation CI
job is failing with errors like `External link
https://rubydoc.brew.sh/Formula#revision=-class_method failed:
https://rubydoc.brew.sh/Formula exists, but the hash
'revision=-class_method' does not`. This updates the URLs to remove
`%3D` accordingly.