docs: Remove references to header_id.md page.

The page was removed along with the extension in 1127013.

Also ensure any future MkDocs warnings cause the build to fail in the tests
so we don't introduce similar errors in the future.

1 files changed, 1 insertions, 1 deletions

diff --git a/checkspelling.sh b/checkspelling.sh
index ac794f7..acd504e 100755
--- a/checkspelling.sh
+++ b/checkspelling.sh
@@ -1,7 +1,7 @@
 #!/bin/bash
 
 echo "Building docs..."
-mkdocs build
+mkdocs build --strict
 if [ $? -ne 0 ]; then
     exit 1
 fi