try using pip environment instead of mamba for RTD build

.readthedocs.yaml

@@ -2,23 +2,20 @@ version: 2
 
 build:
   apt_packages:
-    - "graphviz"
-  os: "ubuntu-24.04"
+    - graphviz
+  os: ubuntu-lts-latest
   tools:
-    python: "mambaforge-4.10"
+    python: latest
   jobs:
     post_checkout:
       - git fetch --unshallow || true
       - git config remote.origin.fetch '+refs/heads/*:refs/remotes/origin/*' || true
       - git fetch --all --tags || true
     pre_install:
-      - git update-index --assume-unchanged docs/rtd_environment.yaml docs/conf.py
+      - git update-index --assume-unchanged docs/conf.py
     post_install:
       - git describe --exact-match || towncrier build --keep
 
-conda:
-  environment: docs/rtd_environment.yaml
-
 sphinx:
   builder: html
   fail_on_warning: true

pyproject.toml

@@ -32,6 +32,7 @@ docs = [
   "graphviz",
   "sphinx-inline-tabs",
   'tomli; python_version < "3.11"',
+  "towncrier",
   "furo",
 ]
 http = ["fsspec[http]>=2022.8.2"]