Drop support for Sphinx 5

Author: AA-Turner

.github/workflows/workflow.yml

@@ -75,8 +75,7 @@ jobs:
           - "3.12"
           - "3.13"
         sphinx-version:
-          - ">=5,<6"
-          - ">=6a0,<7"
+          - ">=6,<7"
           - ">=7,<8"
           - ">=8,<9"
         os:
@@ -94,8 +93,6 @@ jobs:
             os: "macos-latest"
           - python-version: "pypy3.9"
             sphinx-version: ">=8,<9"
-          - python-version: "3.13"
-            sphinx-version: ">=5,<6"
     steps:
       - uses: actions/checkout@v4
       - name: Set up Python ${{ matrix.python-version }}

docs/requirements.txt

@@ -1,6 +1,6 @@
-myst-parser==0.18.1
-furo==2022.9.29
-sphinx==5.2.3
+myst-parser>=4
+furo>=2024
+sphinx~=8.1.0
 sphinx-design
 ./
-matplotlib
+matplotlib

pyproject.toml

@@ -38,7 +38,7 @@ classifiers = [
     "Topic :: Utilities",
 ]
 dependencies = [
-    "Sphinx>=5.0",
+    "Sphinx>=6.0",
 ]
 dynamic = ["version"]