docs: replace broken environment-variables docs link (#1653)

Author: MikeMcC399

README.md

@@ -335,7 +335,7 @@ jobs:
           env: host=api.dev.local,port=4222
 ```
 
-When passing the environment variables this way, unfortunately due to GitHub Actions syntax, the variables should be listed in a single line, which can be hard to read. As an alternative, you can use the step's `env` block where every variable can be set on its own line. In this case, you should prefix every variable with `CYPRESS_` because such variables [are loaded by Cypress automatically](https://on.cypress.io/environment-variables). The above code example is equivalent to:
+When passing the environment variables this way, unfortunately due to GitHub Actions syntax, the variables should be listed in a single line, which can be hard to read. As an alternative, you can use the step's `env` block where every variable can be set on its own line. In this case, you should prefix every variable with `CYPRESS_` because such variables [are loaded by Cypress automatically](https://docs.cypress.io/app/guides/environment-variables). The above code example is equivalent to:
 
 ```yml
 name: Cypress tests