CI: treat documentation warnings as errors

We do not want to merge documentation that produces Sphinx warnings.

scripts/kernel-doc uses environment variable KDOC_WERROR to determine
if warnings should be treated as errors.

Reported-by: Tom Rini <trini@konsulko.com>
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

.azure-pipelines.yml

@@ -89,7 +89,7 @@ stages:
           virtualenv -p /usr/bin/python3 /tmp/venvhtml
           . /tmp/venvhtml/bin/activate
           pip install -r doc/sphinx/requirements.txt
-          make htmldocs
+          make htmldocs KDOC_WERROR=1
           make infodocs
 
   - job: todo

.gitlab-ci.yml

@@ -171,7 +171,7 @@ docs:
     - virtualenv -p /usr/bin/python3 /tmp/venvhtml
     - . /tmp/venvhtml/bin/activate
     - pip install -r doc/sphinx/requirements.txt
-    - make htmldocs
+    - make htmldocs KDOC_WERROR=1
     - make infodocs
 
 # some statistics about the code base