Merge bitcoin/bitcoin#23506: test: Make more shell scripts verifiable by the `shellcheck` tool

a3f61676e8 test: Make more shell scripts verifiable by the `shellcheck` tool (Hennadii Stepanov)

Pull request description:

  Some shell scripts from `contrib/guix` and `contrib/shell` are not verifiable by the `shellcheck` tool for the following reasons:
  - they have no extension (see 4eccf063b2 from bitcoin/bitcoin#21375)
  - they have the `.bash` extension while `.sh` is expected

  This PR adds these scripts to the input for the `shellcheck` tool, and it fixes discovered `shellcheck` warnings.

ACKs for top commit:
  dongcarl:
    Code Review ACK a3f61676e8, this is a good robustness improvement for our shell scripts.
  jamesob:
    crACK a3f61676e8

Tree-SHA512: 6703f5369d9c04c1a174491f381afa5ec2cc4d37321c1b93615abcdde4dfd3caae82868b699c25b72132d8c8c6f2e9cf24d38eb180ed4d0f0584d8c282e58935

contrib/guix/libexec/prelude.bash

@@ -2,10 +2,10 @@
 export LC_ALL=C
 set -e -o pipefail
 
-# shellcheck source=../../shell/realpath.bash
+# shellcheck source=contrib/shell/realpath.bash
 source contrib/shell/realpath.bash
 
-# shellcheck source=../../shell/git-utils.bash
+# shellcheck source=contrib/shell/git-utils.bash
 source contrib/shell/git-utils.bash
 
 ################

test/lint/lint-shell.sh

@@ -20,12 +20,13 @@ if ! command -v shellcheck > /dev/null; then
     exit $EXIT_CODE
 fi
 
-SHELLCHECK_CMD=(shellcheck --external-sources --check-sourced)
+SHELLCHECK_CMD=(shellcheck --external-sources --check-sourced --source-path=SCRIPTDIR)
 EXCLUDE="--exclude=$(IFS=','; echo "${disabled[*]}")"
 # Check shellcheck directive used for sourced files
 mapfile -t SOURCED_FILES < <(git ls-files | xargs gawk '/^# shellcheck shell=/ {print FILENAME} {nextfile}')
+mapfile -t GUIX_FILES < <(git ls-files contrib/guix contrib/shell | xargs gawk '/^#!\/usr\/bin\/env bash/ {print FILENAME} {nextfile}')
 mapfile -t FILES < <(git ls-files -- '*.sh' | grep -vE 'src/(leveldb|secp256k1|minisketch|univalue)/')
-if ! "${SHELLCHECK_CMD[@]}" "$EXCLUDE" "${SOURCED_FILES[@]}" "${FILES[@]}"; then
+if ! "${SHELLCHECK_CMD[@]}" "$EXCLUDE" "${SOURCED_FILES[@]}" "${GUIX_FILES[@]}" "${FILES[@]}"; then
     EXIT_CODE=1
 fi