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/http3-linux.yml

@@ -587,8 +587,7 @@ jobs:
           cargo build -v --package quiche --release --features ffi,pkg-config-meta,qlog --verbose
           ln -s libquiche.so target/release/libquiche.so.0
           mkdir -v quiche/deps/boringssl/src/lib
-          # shellcheck disable=SC2046
-          ln -vnf $(find target/release -name libcrypto.a -o -name libssl.a) quiche/deps/boringssl/src/lib/
+          find target/release \( -name libcrypto.a -o -name libssl.a \) -exec ln -vnf '{}' quiche/deps/boringssl/src/lib \;
 
           # include dir
           # /home/runner/quiche/quiche/deps/boringssl/src/include