Clean up old requirements text files references in workflows and docs

* Removed references to `requirements.txt` in GitHub Actions workflows.
* Updated `mkdocs-deploy.yml` and `main.yml` to install dependencies using `pyproject.toml`.
* Cleaned up documentation to remove mentions of the `requirements` folder.

.github/workflows/main.yml

@@ -28,7 +28,6 @@ jobs:
         python-version: ${{ matrix.python-version }}
         allow-prereleases: true
         cache: 'pip'
-        cache-dependency-path: 'requirements/*.txt'
 
     - name: Upgrade packaging tools
       run: python -m pip install --upgrade pip setuptools virtualenv wheel
@@ -60,7 +59,7 @@ jobs:
         python-version: '3.13'
 
     - name: Install dependencies
-      run: pip install . --group docs
+      run: pip install --group docs
     
     # Start mkdocs server and wait for it to be ready
     - run: mkdocs serve &

.github/workflows/mkdocs-deploy.yml

@@ -7,7 +7,7 @@ on:
     paths:
       - docs/**
       - docs_theme/**
-      - requirements/requirements-documentation.txt
+      - pyproject.toml
       - mkdocs.yml
       - .github/workflows/mkdocs-deploy.yml
 
@@ -25,5 +25,5 @@ jobs:
       - uses: actions/setup-python@v6
         with:
           python-version: 3.x
-      - run: pip install -r requirements/requirements-documentation.txt
+      - run: pip install --group docs
       - run: mkdocs gh-deploy

docs/community/project-management.md

@@ -81,14 +81,6 @@ When pushing the release to PyPI ensure that your environment has been installed
 
 ---
 
-## Project requirements
-
-All our test requirements are pinned to exact versions, in order to ensure that our test runs are reproducible. We maintain the requirements in the `requirements` directory. The requirements files are referenced from the `tox.ini` configuration file, ensuring we have a single source of truth for package versions used in testing.
-
-Package upgrades should generally be treated as isolated pull requests. You can check if there are any packages available at a newer version, by using the `pip list --outdated`.
-
----
-
 ## Project ownership
 
 The PyPI package is owned by `@tomchristie`. As a backup `@j4mie` also has ownership of the package.