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/spacecheck.pl

@@ -88,11 +88,11 @@ sub eol_detect {
 
 my $issues = 0;
 
-open my $git_ls_files, '-|', 'git ls-files' or die "Failed running git ls-files: $!";
+open(my $git_ls_files, '-|', 'git ls-files') or die "Failed running git ls-files: $!";
 while(my $filename = <$git_ls_files>) {
     chomp $filename;
 
-    open my $fh, '<', $filename or die "Cannot open '$filename': $!";
+    open(my $fh, '<', $filename) or die "Cannot open '$filename': $!";
     my $content = do { local $/; <$fh> };
     close $fh;