ci: Set PATH inside the CI env

This is needed for the next commit.

This also requires dropping CI_RETRY from the docker build step, which
is fine, because CI_RETRY should be called inside the build script, not
outside.

Also, fix a doc typo.

ci/lint/04_install.sh

@@ -6,6 +6,8 @@
 
 export LC_ALL=C
 
+export PATH=$PWD/ci/retry:$PATH
+
 ${CI_RETRY_EXE} apt-get update
 # Lint dependencies:
 # - curl/xz-utils (to install shellcheck)