Downgrade twine to version <6.

There is a bug in the jazzband website which does not support newer metadata versions.

Author: mattseymour

.github/workflows/release.yml

@@ -23,7 +23,7 @@ jobs:
       - name: Install dependencies
         run: |
           python -m pip install -U pip
-          python -m pip install -U setuptools wheel twine
+          python -m pip install -U setuptools wheel "twine<6"
 
       - name: Build package
         run: |