fix button text on dev version [skip github][skip azp]

Author: drammock

doc/conf.py

@@ -614,10 +614,12 @@ def append_attr_meth_examples(app, what, name, obj, options, lines):
 xl = '5'
 xxl = '6'
 # variables to pass to HTML templating engine
+switcher_version_match = 'dev' if release.endswith('dev0') else version
 html_context = {
     'build_dev_html': bool(int(os.environ.get('BUILD_DEV_HTML', False))),
     'switcher_json_url': 'https://mne.tools/dev/_static/versions.json',
     'switcher_template_url': 'https://mne.tools/{version}/',
+    'switcher_version_match': switcher_version_match,
     'funders': [
         dict(img='nih.png', size='3', title='National Institutes of Health'),
         dict(img='nsf.png', size='3.5',