feat: add output for last release version

E.g. helpful to use in CI pipelines where versions are not committed to
the repository.

README.md

@@ -216,6 +216,7 @@ steps:
 | new_release_patch_version | Patch version of the new release. (e.g. `0`) |
 | new_release_channel       | The distribution channel on which the last release was initially made available (undefined for the default distribution channel). |
 | new_release_notes         | The release notes for the new release. |
+| last_release_version      | Version of the previous release, if there was one. (e.g. `1.2.0`) |
 
 #### Using Output Variables:
 ```yaml

src/outputs.json

@@ -5,5 +5,6 @@
   "new_release_minor_version": "new_release_minor_version",
   "new_release_patch_version": "new_release_patch_version",
   "new_release_channel": "new_release_channel",
-  "new_release_notes": "new_release_notes"
+  "new_release_notes": "new_release_notes",
+  "last_release_version": "last_release_version"
 }

src/windUpJob.task.js

@@ -40,4 +40,5 @@ module.exports = async (result) => {
   core.setOutput(outputs.new_release_patch_version, patch);
   core.setOutput(outputs.new_release_channel, channel);
   core.setOutput(outputs.new_release_notes, notes);
+  core.setOutput(outputs.last_release_version, lastRelease.version)
 };