Merge bitcoin/bitcoin#26908: ci: Add missing lint dependency (gpg)

fa87d71 ci: Add missing lint dependency (MarcoFalke)

Pull request description:

  Also, document each dependency.

  Adding `gpg` avoids errors when running a release or dev branch in the CI:

  https://github.com/bitcoin/bitcoin/blob/01ec5308bf616740c804247043046b23b483df5c/ci/lint/06_script.sh#L30-L42

  ```
  bash: line 1: gpg: command not found
  ```

  https://cirrus-ci.com/task/4582854860996608?logs=lint#L185

ACKs for top commit:
  hebasto:
    ACK fa87d71

Tree-SHA512: 869a3d2feab764b2c8d47d481359680a1d2c54a33b13ca26c5f8ce56cf2f368d4c74637dcbc53fdbf323f10940965c1c0e592e2fb4ce725d5cd467e77e62b6e5

Author: fanquake

ci/lint/04_install.sh

@@ -7,7 +7,11 @@
 export LC_ALL=C
 
 ${CI_RETRY_EXE} apt-get update
-${CI_RETRY_EXE} apt-get install -y curl git gawk jq xz-utils
+# Lint dependencies:
+# - curl/xz-utils (to install shellcheck)
+# - git (used in many lint scripts)
+# - gpg (used by verify-commits)
+${CI_RETRY_EXE} apt-get install -y curl xz-utils git gpg
 
 PYTHON_PATH=/tmp/python
 if [ ! -d "${PYTHON_PATH}/bin" ]; then