`superfences` and `terraform` example generates duplicate output

Contribution guidelines

• I’ve read the contribution guidelines and wholeheartedly agree

I’ve found a bug and checked that …

• … the problem doesn’t occur with the mkdocs or readthedocs themes
• … the problem persists when all overrides are removed, i.e. custom_dir, extra_javascript and extra_css
• … the documentation does not mention anything about my problem
• … there are no open or closed issues that are related to my problem

Description

When creating an example with << in to, the contents after is include twice ie:

```teraform
<<a
x
```

Expected behaviour

Output should be:

<<a
x

Actual behaviour

renders as

<<a
x
x

Steps to reproduce

1. Create new blank project

python3 -m venv .venv
source .venv/bin/activate
pip install mkdocs-material
mkdocs new .

1. Update mkdocs.yml to be

site_name: Example
theme:
  name: material
markdown_extensions:
  - pymdownx.superfences

1. update index.md to be

```teraform
<<a
x
```

1. run mkdocs serve

Output will be

<<a
x
x

Or

1. git clone https://github.com/michaelbrewer/mkdocs-github-issue.git
2. make dev serve

Package versions

• Python: python --version:
  Python 3.9.13
• MkDocs: mkdocs --version mkdocs, version 1.3.1 from /Users/michaelbrewer/projects/python/mkdocs-eof/.venv/lib/python3.9/site-packages/mkdocs (Python 3.9)
• Material: pip show mkdocs-material | grep -E ^Version Version: 8.3.9

Configuration

site_name: Example
theme:
  name: material
markdown_extensions:
  - pymdownx.superfences

System information

• Operating system: …
• Browser: …

[facelessuser]

Awesome! Glad we were able to narrow it down.

[squidfunk]

Thanks for your time researching, @facelessuser and @michaelbrewer. Closing as upstream issue.