Fix tag creation (#39)

Author: max-leuthaeuser

.github/workflows/pr.yml

@@ -59,4 +59,4 @@ jobs:
           repo_token: ${{ secrets.GITHUB_TOKEN }}
           file: astgen-*
           target_commit: ${{ github.head_ref || github.ref_name }}
-          tag: v${{ env.ASTGEN_VERSION }}
+          tag: v${{ env.ASTGEN_VERSION }}-prerelease

.github/workflows/release.yml

@@ -60,5 +60,4 @@ jobs:
           file_glob: true
           repo_token: ${{ secrets.GITHUB_TOKEN }}
           file: astgen-*
-          target_commit: ${{ github.ref }}
           tag: v${{ env.ASTGEN_VERSION }}