scripts: fix shellcheck SC2046 warnings

Fix SC2046: "Quote this to prevent word splitting."
Ref: https://www.shellcheck.net/wiki/SC2046

Also:
- shellcheck.sh: add `set -eu`.
- shellcheck.sh, yamlcheck.sh: always run from repo root.
- pass `--` before passing the list of files, where missing.
- badwords.pl, cleancmd.pl: rework to accept `git ls-files` arguments.
  Requires Perl 5.22+ (2015-Jun-01) on Windows.
  Ref: https://perldoc.perl.org/functions/open
- INTERNALS.md: require Perl 5.22 on Windows.
- spacecheck.pl: formatting.
- GHA/http3-linux: rework command to avoid SC2046.
- stop suppressing SC2046 warnings.

The yamlcheck.sh issue reported-by: Stanislav Fort (Aisle Research)
Ref: 20251109163515_6eb31da3-deb2-4f4d-8327-935904f27da5

Closes #19432

.github/scripts/shellcheck.sh

@@ -3,7 +3,11 @@
 #
 # SPDX-License-Identifier: curl
 
-# shellcheck disable=SC2046
-shellcheck --exclude=1091 \
+set -eu
+
+cd "$(dirname "${0}")"/../..
+
+git grep -z -l -E '^#!(/usr/bin/env bash|/bin/sh|/bin/bash)' | xargs -0 -r \
+shellcheck --exclude=1091,2248 \
   --enable=avoid-nullary-conditions,deprecate-which \
-  $(grep -l -E '^#!(/usr/bin/env bash|/bin/sh|/bin/bash)' $(git ls-files))
+  --