Change hyphents in action inputs to underscores

The GitHub Action docs
[illustrate](https://docs.github.com/en/actions/creating-actions/metadata-syntax-for-github-actions#example-specifying-inputs)
using hyphens in input names, and then document that names like
`octocat-eye-color` are converted to environment variables like
`INPUT_OCTOCAT-EYE-COLOR`, but these environment variable names
are [not POSIX compliant](https://stackoverflow.com/a/36992531/2019542)
and can't be accessed in many shells.
They've [known about this](actions/toolkit#629) for two years.
Grrrr.

action.yml

@@ -6,22 +6,22 @@ inputs:
     description:
       Subcommand to perform [borg_the_docs, update_pages].
     required: true
-  docs-folder:
+  docs_folder:
     description:
       The folder containing your sphinx docs.
     required: true
     default: "docs/"
-  default-branch:
+  default_branch:
     description:
       The default branch configured in GitHub.
     required: false
     default: "main"
-  pages-branch:
+  pages_branch:
     description: 
       The branch linked to your documentation server.
     required: false
     default: 'nist-pages'
-  pages-url:
+  pages_url:
     description:
       URL of web server for served documentation.
     required: false

entrypoint.py

@@ -8,21 +8,15 @@
 
 def main():
     action = os.environ['INPUT_ACTION']
-    docs = SphinxDocs(docs_dir=os.environ['INPUT_DOCS-FOLDER'])
-
-#     # Install any requirements for documentation.
-#     # Adapted from ammaraskar/sphinx-action
-#     requirements = os.path.join(docs.docs_dir, "requirements.txt")
-#     if os.path.exists(requirements):
-#         subprocess.check_call(["pip", "install", "-r", requirements])
+    docs = SphinxDocs(docs_dir=os.environ['INPUT_DOCS_FOLDER'])
 
     if action == 'update_pages':
         repo = Repository(server_url=os.environ['GITHUB_SERVER_URL'],
                           repository=os.environ['GITHUB_REPOSITORY'],
-                          branch=os.environ['INPUT_PAGES-BRANCH'],
-                          default_branch=os.environ['INPUT_DEFAULT-BRANCH'],
+                          branch=os.environ['INPUT_PAGES_BRANCH'],
+                          default_branch=os.environ['INPUT_DEFAULT_BRANCH'],
                           docs=docs,
-                          pages_url=os.environ['INPUT_PAGES-URL'])
+                          pages_url=os.environ['INPUT_PAGES_URL'])
 
         repo.update_pages(branch=os.environ['SANITIZED_REF_NAME'],
                           sha=os.environ['GITHUB_SHA'])

entrypoint.sh

@@ -3,12 +3,12 @@
 echo "::error::`env`"
 echo "::warning::INPUT_ACTION=${INPUT_ACTION}"
 echo "::warning::GITHUB_SHA=${GITHUB_SHA}"
-echo "::warning::INPUT_DOCS-FOLDER=${INPUT_DOCS-FOLDER}"
-echo "::warning::INPUT_DEFAULT-BRANCH=${INPUT_DEFAULT-BRANCH}"
-echo "::warning::INPUT_PAGES-BRANCH=${INPUT_PAGES-BRANCH}"
-echo "::warning::INPUT_PAGES-URL=${INPUT_PAGES-URL}"
+echo "::warning::INPUT_DOCS_FOLDER=${INPUT_DOCS_FOLDER}"
+echo "::warning::INPUT_DEFAULT_BRANCH=${INPUT_DEFAULT_BRANCH}"
+echo "::warning::INPUT_PAGES_BRANCH=${INPUT_PAGES_BRANCH}"
+echo "::warning::INPUT_PAGES_URL=${INPUT_PAGES_URL}"
 
-requirements="${INPUT_DOCS-FOLDER}/requirements.txt"
+requirements="${INPUT_DOCS_FOLDER}/requirements.txt"
 
 echo "::error::requirements=${requirements}"
 if [ -f $requirements ];