Ignore deleted files in docs linting

Otherwise our script will fail if a file gets deleted.

scripts/lint-doc.sh

@@ -92,12 +92,12 @@ then
   echo "Merge request pipeline (detached) detected. Testing all files."
 else
   MERGE_BASE=$(git merge-base ${CI_MERGE_REQUEST_TARGET_BRANCH_SHA} ${CI_MERGE_REQUEST_SOURCE_BRANCH_SHA})
-  if git diff --name-only "${MERGE_BASE}..${CI_MERGE_REQUEST_SOURCE_BRANCH_SHA}" | grep -E "\.vale|\.markdownlint|lint-doc\.sh"
+  if git diff --diff-filter=d --name-only "${MERGE_BASE}..${CI_MERGE_REQUEST_SOURCE_BRANCH_SHA}" | grep -E "\.vale|\.markdownlint|lint-doc\.sh"
   then
     MD_DOC_PATH=${MD_DOC_PATH:-doc}
     echo "Vale, Markdownlint, or lint-doc.sh configuration changed. Testing all files."
   else
-    MD_DOC_PATH=$(git diff --name-only "${MERGE_BASE}..${CI_MERGE_REQUEST_SOURCE_BRANCH_SHA}" 'doc/*.md')
+    MD_DOC_PATH=$(git diff --diff-filter=d --name-only "${MERGE_BASE}..${CI_MERGE_REQUEST_SOURCE_BRANCH_SHA}" -- 'doc/*.md')
     if [ -n "${MD_DOC_PATH}" ]
     then
       echo -e "Merged results pipeline detected. Testing only the following files:\n${MD_DOC_PATH}"