ci: Document the retry script in PATH

The `retry` script is required for CI_RETRY_EXE and there are two ways
to put it into PATH:

* When running in a container engine, by copying it into /usr/bin
* When running without a container engine, by prepending its location to PATH

ci/test/02_run_container.py

@@ -56,6 +56,9 @@ def main():
                 os.environ["PREVIOUS_RELEASES_DIR"],
         ]:
             Path(create_dir).mkdir(parents=True, exist_ok=True)
+
+        # Modify PATH to prepend the retry script, needed for CI_RETRY_EXE
+        os.environ["PATH"] = f"{os.environ['BASE_ROOT_DIR']}/ci/retry:{os.environ['PATH']}"
     else:
         CI_IMAGE_LABEL = "bitcoin-ci-test"
 

ci/test/02_run_container.sh

@@ -13,7 +13,7 @@ if [ -z "$DANGER_RUN_CI_ON_HOST" ]; then
 fi
 
 CI_EXEC () {
-  $CI_EXEC_CMD_PREFIX bash -c "export PATH=\"/path_with space:${BASE_ROOT_DIR}/ci/retry:\$PATH\" && cd \"${BASE_ROOT_DIR}\" && $*"
+  $CI_EXEC_CMD_PREFIX bash -c "export PATH=\"/path_with space:\$PATH\" && cd \"${BASE_ROOT_DIR}\" && $*"
 }
 export -f CI_EXEC