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/yamlcheck.sh

@@ -5,9 +5,11 @@
 
 set -eu
 
-# shellcheck disable=SC2046
+cd "$(dirname "${0}")"/../..
+
+git ls-files '*.yaml' '*.yml' -z | xargs -0 -r \
 yamllint \
   --format standard \
   --strict \
-  --config-data "$(dirname "$0")/yamlcheck.yaml" \
-  $(git ls-files '*.yaml' '*.yml')
+  --config-data .github/scripts/yamlcheck.yaml \
+  --