Pin python libraries

Use pinned `requirements.txt` and an additional `constraints.txt` file
to ensure pip constructs a viable build environment. The upstream
version (see [1]) partially depends on the distribution repositories
for versioning via packages like `python3-doc8` but I went though and
pinned everything in the `pip` files instead to create a single source
of truth independent of system packages.

Based on [1] by @clalancette upstream in `ros2/ros2_documentation`

[1] ros2/ros2_documentation@e43347d

.github/workflows/spaceros.yml

@@ -20,7 +20,7 @@ jobs:
 
       - name: Install dependencies with pip
         run: |
-          pip install --no-warn-script-location --user --upgrade -r requirements.txt
+          pip install --no-warn-script-location --user -r requirements.txt -c constraints.txt
 
       - name: Build
         run: make html
@@ -44,7 +44,7 @@ jobs:
 
       - name: Install dependencies with pip
         run: |
-          pip install --no-warn-script-location --user --upgrade -r requirements.txt
+          pip install --no-warn-script-location --user -r requirements.txt -c constraints.txt
 
       - name: Build
         run: make multiversion

constraints.txt

@@ -0,0 +1,33 @@
+Jinja2==3.0.3
+MarkupSafe==2.0.1
+Pygments==2.11.2
+alabaster==0.7.12
+babel==2.8.0
+certifi==2020.6.20
+chardet==4.0.0
+imagesize==1.3.0
+importlib-metadata==4.6.4
+more-itertools==8.10.0
+packaging==21.3
+pbr==5.8.0
+pip==22.0.2
+pyparsing==2.4.7
+pytz==2022.1
+requests==2.25.1
+restructuredtext-lint==1.3.2
+roman==3.3
+setuptools==59.6.0
+six==1.16.0
+snowballstemmer==2.2.0
+doc8==0.8.1
+docutils==0.16.0
+Sphinx==4.3.2
+sphinx-copybutton==0.4.0
+sphinx-multiversion==0.2.4
+sphinx-rtd-theme==1.0.0
+sphinx-sitemap==2.3.0
+sphinx-tabs==3.2.0
+stevedore==3.5.0
+urllib3==1.26.5
+wheel==0.37.1
+zipp==1.0.0

docker/image/Dockerfile

@@ -25,4 +25,4 @@ WORKDIR /tmp/doc_repository
 
 USER $user
 
-CMD pip3 install --no-warn-script-location --user --upgrade -r requirements.txt && make multiversion
+CMD pip3 install --no-warn-script-location --user -r requirements.txt -c constraints.txt && make multiversion

requirements.txt

@@ -1,9 +1,9 @@
-doc8
-docutils==0.16
-pip
-sphinx
-sphinx-copybutton
-sphinx-multiversion
-sphinx-rtd-theme
-sphinx-sitemap
-sphinx-tabs
+doc8==0.8.1
+docutils==0.16.0
+pip==22.0.2
+sphinx==4.3.2
+sphinx-copybutton==0.4.0
+sphinx-multiversion==0.2.4
+sphinx-rtd-theme==1.0.0
+sphinx-sitemap==2.3.0
+sphinx-tabs==3.2.0