Fix release workflow's manifest-commit checkout and correct 0.3.0.0 checksum

The "Commit updated manifest to master" step left manifest.json dirty
(modified during the tag checkout by package-release.sh) and then tried to
git checkout master, which git correctly refused -- that's the CI failure
from the v0.3.0.0 tag push. Discard the working-tree manifest.json before
switching branches, matching the /tmp copy-then-restore pattern already used
for carrying the update across.

Also corrects the 0.3.0.0 manifest entry itself: it had been hand-edited
locally with 0.2.0.0's leftover checksum instead of the real zip's hash, and
had dropped the 0.2.0.0 history entry entirely instead of appending. Rebuilt
via update_manifest.py against origin/master's manifest.json using the
actual checksum of the already-uploaded v0.3.0.0 release asset.

.github/workflows/release.yml

@@ -78,6 +78,7 @@ jobs:
           VERSION: ${{ steps.meta.outputs.VERSION }}
         run: |
           cp manifest.json /tmp/manifest.json
+          git checkout -- manifest.json
           git fetch origin master
           git checkout master
           cp /tmp/manifest.json manifest.json