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/workflows/checksrc.yml

@@ -164,7 +164,4 @@ jobs:
 
       # we allow some extra in source code
       - name: 'badwords'
-        run: |
-          # shellcheck disable=SC2046
-          grep -Ev '(\\bwill| url | dir )' .github/scripts/badwords.txt | \
-          .github/scripts/badwords.pl $(git ls-files -- src lib include)
+        run: grep -Ev '(\\bwill| url | dir )' .github/scripts/badwords.txt | .github/scripts/badwords.pl src lib include