ci: use built-in Gitea Actions token for release publish

Drops the need for a manually-managed RELEASE_TOKEN secret; adds
contents:write permission so github.token can create the release.

.gitea/workflows/release.yml

@@ -5,6 +5,9 @@ on:
     tags:
       - 'v*.*.*'
 
+permissions:
+  contents: write
+
 jobs:
   build:
     runs-on: windows
@@ -70,7 +73,7 @@ jobs:
       - name: Publish Gitea release
         shell: pwsh
         env:
-          TOKEN: ${{ secrets.RELEASE_TOKEN }}
+          TOKEN: ${{ github.token }}
         run: |
           $ver = '${{ steps.ver.outputs.version }}'
           $tag = "v$ver"