meson: bump minimum version to 0.50.0
WARNING: Project specifies a minimum meson_version '>= 0.49.0' but uses features which were added in newer versions: * 0.50.0: {'install arg in configure_file'}
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WARNING: Project specifies a minimum meson_version '>= 0.49.0' but uses features which were added in newer versions: * 0.50.0: {'install arg in configure_file'}