🪲 [Fix]: Suppress output of functions for revoking access tokens (#452)

## Description

This pull request makes small adjustments to improve code clarity and
ensure consistent handling of unused return values. Specifically, it
updates two functions to explicitly discard the output of the
`Invoke-GitHubAPI` command by assigning it to `$null`.

Changes to improve code clarity:

* [`src/functions/private/Apps/GitHub
Apps/Revoke-GitHubAppInstallationAccessToken.ps1`](diffhunk://#diff-fd0c42ecf8245c045d9e3798af80e494cd944a2e8ba180bf5719f381f517f689L39-R39):
Updated the `Revoke-GitHubAppInstallationAccessToken` function to assign
the return value of `Invoke-GitHubAPI` to `$null`, ensuring unused
output is explicitly discarded.
*
[`src/functions/public/Auth/Revoke-GitHubAccessToken.ps1`](diffhunk://#diff-9be3d5b3b006ef480e23f78ee1fa7cb03d19f8973cc39eab75c452e8f59c3730L47-R47):
Updated the `Revoke-GitHubAccessToken` function to assign the return
value of `Invoke-GitHubAPI` to `$null`, maintaining consistency in
handling unused outputs.

## Type of change

<!-- Use the check-boxes [x] on the options that are relevant. -->

- [ ] 📖 [Docs]
- [x] 🪲 [Fix]
- [ ] 🩹 [Patch]
- [ ] ⚠️ [Security fix]
- [ ] 🚀 [Feature]
- [ ] 🌟 [Breaking change]

## Checklist

<!-- Use the check-boxes [x] on the options that are relevant. -->

- [x] I have performed a self-review of my own code
- [x] I have commented my code, particularly in hard-to-understand areas

Author: MariusStorhaug

src/functions/private/Apps/GitHub Apps/Revoke-GitHubAppInstallationAccessToken.ps1

@@ -36,7 +36,7 @@ function Revoke-GitHubAppInstallationAccessToken {
         }
 
         if ($PSCmdlet.ShouldProcess('GitHub App installation access token', 'Revoke')) {
-            Invoke-GitHubAPI @InputObject
+            $null = Invoke-GitHubAPI @InputObject
         }
     }
 

src/functions/public/Auth/Revoke-GitHubAccessToken.ps1

@@ -44,7 +44,7 @@
                 Anonymous   = $true
             }
             if ($PSCmdlet.ShouldProcess('Tokens', 'Revoke')) {
-                Invoke-GitHubAPI @InputObject
+                $null = Invoke-GitHubAPI @InputObject
             }
         }
         Write-Debug "[$stackPath] - End"