use towncrier checks instead of custom code.

.github/workflows/test.yaml

@@ -273,9 +273,10 @@ jobs:
 
     steps:
     - uses: actions/checkout@v3
-      with:
-        # Need history on all branches for newsfragment to work.
-        fetch-depth: 0
+
+    - name: Get main branch for any diff checks
+      run: |
+        git fetch origin trunk:trunk
 
     - name: Set up Python
       uses: actions/setup-python@v4
@@ -289,20 +290,7 @@ jobs:
     - name: Run the checks
       run: |
         python --version
-        tox --parallel -e lint,mypy
-
-    - name: Revert merge commit for a release branch
-      if: github.event_name == 'pull_request' && startsWith(github.head_ref, 'release-')
-      env:
-        BRANCH_SHA: ${{ github.event.after }}
-        BRANCH_NAME: ${{ github.head_ref }}
-      run: |
-        git checkout -b $BRANCH_NAME
-        git reset --hard $BRANCH_SHA
-
-    - name: Newsfragment
-      run: |
-        tox -q -e newsfragment
+        tox --parallel -e lint,mypy,newsfragment
 
 
   # Used to validate the narrative and API docs.

NEWS.rst

@@ -8,6 +8,48 @@ https://twisted.org/trac/ticket/<number>
 
 .. towncrier release notes start
 
+Twisted 23.8.0.rc1 (2023-08-18)
+===============================
+
+No significant changes.
+
+
+Conch
+-----
+
+No significant changes.
+
+
+Web
+---
+
+No significant changes.
+
+
+Mail
+----
+
+No significant changes.
+
+
+Words
+-----
+
+No significant changes.
+
+
+Names
+-----
+
+No significant changes.
+
+
+Trial
+-----
+
+No significant changes.
+
+
 Twisted 23.8.0.rc1 (2023-08-17)
 ===============================
 

tox.ini

@@ -62,6 +62,7 @@ extras =
     serial: serial
 
     {withcov}: dev
+    newsfragment: dev
 
 ;; dependencies that are not specified as extras
 deps =
@@ -132,7 +133,7 @@ commands =
     # FIXME:https://github.com/twisted/twisted/issues/11583
     # With latest towncrier we should be amble to just use towncrier included
     # `check` tool.
-    newsfragment: python {toxinidir}/bin/admin/check-newsfragment "{toxinidir}"
+    newsfragment: python -m towncrier check --compare-with=trunk
 
 
 [testenv:towncrier]