Simplify interactions with githubRelease extension properties

[tylerbertrand]

Hi 👋

This PR would make the change to use Strings over CharSequence for githubRelease extension properties.

Interacting with CharSequence githubRelease extension properties can result in some syntactical overhead. As an example, when using the tagName from the githubRelease extension, passing that value to another API requires converting that value to a String. This applies to both Groovy and Kotlin.

Groovy:

tagName = githubRelease.tagName.map { it.toString() }

Kotlin:

tagName.set(githubRelease.tagName.map { it.toString() })

This tends to add some amount of noise to the code as most APIs use Strings for such things. With this PR, the above code snippets would be simplified to the following:

Groovy:

tagName = githubRelease.tagName

Kotlin:

tagName.set(githubRelease.tagName)

Gradle build scan: https://scans.gradle.com/s/butpox5cvgpqo