Pin numpy<2, delete old doc build

.gitignore

@@ -11,6 +11,7 @@ pysynphot/version.py
 
 # Sphinx
 _build
+doc/tsrs/bandpar_comparison/build
 
 # Packages/installer info
 *.egg*

.readthedocs.yml

@@ -2,15 +2,20 @@
 # See https://docs.readthedocs.io/en/stable/config-file/v2.html for details
 version: 2
 
+build:
+  os: ubuntu-22.04
+  apt_packages:
+    - graphviz
+  tools:
+    python: "3.11"
+
 sphinx:
   builder: html
   configuration: doc/source/conf.py
   fail_on_warning: true
 
 # Set the version of Python and requirements required to build your docs
 python:
-  version: 3.8
-  system_packages: false
   install:
     - requirements: doc/rtd-pip-requirements
     - method: pip

doc/rtd-pip-requirements

@@ -1 +1 @@
-sphinx>=2
+sphinx>=2,<7