upgrade to polkadot v1.8.0 #744

Job	Run time
build	23m 58s
build-try-runtime-and-benchmarks	20m 30s
Build Runtimes (encointer-node-notee)	13m 58s
Cancel Previous Runs	4s
cargo-toml-fmt	10s
unit-tests	18m 27s
Rust check +nightly fmt --all -- --check (x86_64-unknown-linux-gnu)	1m 22s
Rust check clippy -p encointer-client-notee (x86_64-unknown-linux-gnu)	11m 48s
test_bootstrap_demo_community.sh	35s
test_bot_community.sh	39s
test_register_business.sh	54s
Draft Release	0s
Publish Runtimes	0s
	1h 32m 25s

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