The heredoc inside the YAML block scalar (|) broke YAML parsing because
the heredoc body lines (#!/bin/bash, exec lua...) were at column 0,
which YAML interpreted as top-level keys. The ':' in the exec line
triggered 'could not find expected ':'' parse errors.
Replace with printf to keep the entire build script as properly-indented
YAML block scalar content. This also fixes the mason UI crash where the
newline-containing error message triggered 'replacement string item
contains newlines' in nvim_buf_set_lines.