Drop workflow_dispatch build method

It causes unnecessary complication: because `python -m build` needs `git tag` to have been run already, so we needed to awkwardly both run that ourselves and then feed it into action-gh-release which redoes the tagging.

Instead, make only one way to do it: click to the Releases page and make a release from there, which guarantees the tag to be pre-created.

.github/workflows/publish.yml

@@ -7,13 +7,6 @@ on:
   release:
     types: [published]
 
-  # publish from the Actions page:
-  workflow_dispatch:
-    inputs:
-      version:
-        description: 'Version'
-        required: true
-
 jobs:
   publish:
     name: Publish Package
@@ -23,14 +16,6 @@ jobs:
     steps:
     - uses: actions/checkout@v3
 
-    - name: Create given tag
-      # because we use setuptools_scm, the tag needs to exist before running `build`
-      # this is a bit redundant because softprops/action-gh-release will recreate the
-      # same tag, on github
-      if: github.event.inputs.version
-      run: |
-        git tag -f "${{ github.event.inputs.version }}"
-
     - uses: actions/setup-python@v3
 
     - name: Install dependencies
@@ -46,7 +31,6 @@ jobs:
       with:
         files: 'dist/*'
         fail_on_unmatched_files: true
-        tag_name: ${{ github.event.inputs.version }} # in the workflow_dispatch case, make a new tag from the given input; in the published release case, this will be empty and will fall back to updating that release.
 
     - name: Publish to PyPI
       uses: pypa/gh-action-pypi-publish@release/v1