Handle 5.7 Package.resolved format

[finestructure]

Swift 5.7 comes with a new Package.resolved format that we're not handling yet:

{
  ...
  "version" : 2
}

This leads to a blank PR using @MarcoEidinger 's swift-package-dependencies-check workflow.

(Side note: it's probably better in this case for the action not to fail entirely but perhaps it could inject an explanation into the PR text in case swift-release-notes fails.)

[finestructure]

Released as 0.0.7

cc @MarcoEidinger

[MarcoEidinger]

Used in swift-package-dependencies-check workflow with latest 2.3.3 version (to which v2 points to)

cc @finestructure