Revert "Bug 2023603 - Update MyST-Parser to 5.1.0 to fix links with multiple query parameters r=ahal" for causing python failures @ test_site_compatibility.py

This reverts commit 2dd71ebdc3.

docs/config.yml

@@ -135,7 +135,6 @@ allowed_warnings:
     - "WARNING: duplicate label"
     - "WARNING: local id not found in doc"
     - "WARNING: 'myst' cross-reference target not found"
-    - "WARNING: Unknown source document"
     - "WARNING: Lexing literal_block"
     - "WARNING: dot command 'dot' cannot be run \\(needed for graphviz output\\)"
     # Specific warnings allowed when the allow list was created.

python/sites/docs.txt

@@ -1,20 +1,24 @@
-requires-python:>=3.11
+requires-python:>=3.9
 # The following are only required by autodoc
 pth:python/mozpack/test
 pth:tools/lint/eslint/
-pypi:Sphinx==8.2.3
-pypi:boto3==1.38.38
+pypi:Sphinx==7.4.7
+# boto3 and types-requests have incompatible urllib3 requirements in Python 3.9
+# ( as explained in https://bugzilla.mozilla.org/show_bug.cgi?id=1998780#c4 ).
+# "./mach doc --upload" requires boto3, but other "./mach doc" functionality
+# does not. So to support common operations in Python 3.9, make it optional.
+pypi:boto3==1.38.38 ; python_version >= "3.10"
 pypi:fluent.pygments==1.0
 pypi:livereload==2.6.3
 pypi:mots==0.13.1
-pypi:myst-parser==5.1.0
+pypi:myst-parser==2.0
 pypi:pytest==8.4.2
 pypi:pywatchman==1.4.1
 pypi:sphinx-copybutton==0.5.2
-pypi:sphinx-design==0.6.1
+pypi:sphinx-design==0.5.0
 pypi:sphinx-js==4.0.0
 pypi:sphinx-markdown-tables==0.0.17
-pypi:sphinx-rtd-theme==3.0.2
+pypi:sphinx-rtd-theme==2.0.0
 pypi:sphinx-tabs==3.4.7
 pypi:sphinxcontrib-mermaid==1.0.0
 # psutil is needed for autodoc to import mozbuild.doctor and marionette_driver.processhandler

taskcluster/requirements.in

@@ -4,3 +4,5 @@ mozilla-taskgraph==4.1.1
 requests-unixsocket
 taskcluster-taskgraph[orjson,load-image]==20.0.0
 rtoml==0.13.0; python_version >= "3.10"
+# Temporarily resolve conflict with myst-parser 2.0.0 in python/sites/docs.txt
+markdown-it-py < 4