fix: use core.getBooleanInput() to retrieve boolean input values (#223)

This PR switches from evaluating values passed to `skip-token-revoke` as
true if they are truthy in JavaScript, to using `getBooleanInput`. This
change ensures that only proper YAML boolean values are recognized,
preventing unintended evaluations to true.
- The definition of `getBooleanInput` is here: definition of
`core#getBooealnInput` is here:
930c890727/packages/core/src/core.ts (L188-L208)

The documentation states, `"If truthy, the token will not be revoked
when the current job is complete"`, so this change could be considered a
breaking change. This means that if there are users who rely on `truthy`
and expect values like whitespace or `"false"` to be evaluated as true
(though this is likely rare), it would be a breaking change.
- `Boolean(" ")` and `Boolean("false")` are both evaluated as true.

Alternatively, it can simply be considered a fix. How to handle this is
up to the maintainer.

Resolves https://github.com/actions/create-github-app-token/issues/216

README.md

@@ -343,7 +343,7 @@ The reason we define one `permision-<permission name>` input per permission is t
 
 ### `skip-token-revoke`
 
-**Optional:** If truthy, the token will not be revoked when the current job is complete.
+**Optional:** If true, the token will not be revoked when the current job is complete.
 
 ### `github-api-url`
 
@@ -370,7 +370,7 @@ The action creates an installation access token using [the `POST /app/installati
 1. The token is scoped to the current repository or `repositories` if set.
 2. The token inherits all the installation's permissions.
 3. The token is set as output `token` which can be used in subsequent steps.
-4. Unless the `skip-token-revoke` input is set to a truthy value, the token is revoked in the `post` step of the action, which means it cannot be passed to another job.
+4. Unless the `skip-token-revoke` input is set to true, the token is revoked in the `post` step of the action, which means it cannot be passed to another job.
 5. The token is masked, it cannot be logged accidentally.
 
 > [!NOTE]