scripts: pass -- before passing xargs

Also:
- GHA/checkdocs: escape `.` in -E regex expression.

Closes #19076

scripts/cmakelint.sh

@@ -77,4 +77,5 @@ cd "$(dirname "$0")"/..
     --max-branches 12 \
     --max-arguments 5 \
     --max-localvars 15 \
-    --max-statements 50
+    --max-statements 50 \
+    --

scripts/firefox-db2pem.sh

@@ -57,5 +57,5 @@ sed -e 's/ *[CcGTPpu]*,[CcGTPpu]*,[CcGTPpu]* *$//' -e 's/\(.*\)/"\1"/' | \
 sort | \
 while read -r nickname; \
  do echo "$nickname" | sed -e "s/Builtin Object Token://g"; \
- echo "$nickname" | xargs -I{} certutil -d "$db" -L -a -n {} ; \
+ echo "$nickname" | xargs -I{} certutil -d "$db" -L -a -n -- {} ; \
 done >> "$out"

scripts/perlcheck.sh

@@ -48,4 +48,4 @@ echo "parallel: ${procs}"
     # strip off the leading ./ to make the grep regexes work properly
     find . -type f \( -name '*.pl' -o -name '*.pm' \) | sed 's@^\./@@'
   fi
-} | xargs -n 1 -P "${procs}" perl -c -Itests
+} | xargs -n 1 -P "${procs}" perl -c -Itests --