Fix towncrier command

Author: dstansby

.readthedocs.yaml

@@ -6,7 +6,7 @@ build:
     python: "3.12"
   jobs:
     pre_build:
-      - towncrier --build --version Unreleased --yes
+      - towncrier build --version Unreleased --yes
 
 sphinx:
   configuration: docs/conf.py

docs/developers/contributing.rst

@@ -337,7 +337,7 @@ Pre-release
 """""""""""
 1. Make sure that all pull requests which will be included in the release
    have been properly documented as changelog files in :file:`changes`.
-2. Run ``towncrier --build --version x.y.z`` to create the changelog.
+2. Run ``towncrier build --version x.y.z`` to create the changelog.
 
 Releasing
 """""""""