chore: fix github-script invocation (#433)

According to the relesae notes, github.* API methods have been removed and
should instead by accessed by github.rest.*. Use that method to access pull
request information.

Signed-off-by: Will Murphy <will.murphy@anchore.com>

.github/workflows/update-snapshots.yml

@@ -23,7 +23,7 @@ jobs:
             }
             core.info(`Getting PR #${request.pull_number} from ${request.owner}/${request.repo}`)
             try {
-              const result = await github.pulls.get(request)
+              const result = await github.rest.pulls.get(request)
               return result.data
             } catch (err) {
               core.setFailed(`Request failed with error ${err}`)