Remove timestamps from docs/api-reference/*/*.html

If there are 2 or more PR(s) in the queue, they will end up with
conflicts (and rechecks). So let us remove the timestamp entirely
when we generate the files.

Fixes #46814

hack/lib/swagger.sh

@@ -127,13 +127,25 @@ kube::swagger::gen_api_ref_docs() {
   find . -type f | cut -sd / -f 2- | LC_ALL=C sort > .generated_html
   popd > /dev/null
 
+  if LANG=C sed --help 2>&1 | grep -q GNU; then
+    SED="sed"
+  elif which gsed &>/dev/null; then
+    SED="gsed"
+  else
+    echo "Failed to find GNU sed as sed or gsed. If you are on Mac: brew install gnu-sed." >&2
+    exit 1
+  fi
+
   while read file; do
     if [[ -e "${output_dir}/${file}" && -e "${output_tmp}/${file}" ]]; then
       echo "comparing ${output_dir}/${file} with ${output_tmp}/${file}"
 
+      # Remove the timestamp to reduce conflicts in PR(s)
+      $SED -i 's/^Last updated.*$//' "${output_tmp}/${file}"
+
       # By now, the contents should be normalized and stripped of any
       # auto-managed content.
-      if diff -NauprB -I 'Last update' "${output_dir}/${file}" "${output_tmp}/${file}" >/dev/null; then
+      if diff -NauprB "${output_dir}/${file}" "${output_tmp}/${file}" >/dev/null; then
         # actual contents same, overwrite generated with original.
         cp "${output_dir}/${file}" "${output_tmp}/${file}"
       fi