upgrade to polkadot v1.8.0 #746

Job	Run time
Cancel Previous Runs	5s
build	23m 58s
build-try-runtime-and-benchmarks	25m 20s
Build Runtimes (encointer-node-notee)	3m 56s
cargo-toml-fmt	11s
unit-tests	19m 52s
Rust check +nightly fmt --all -- --check (x86_64-unknown-linux-gnu)	1m 2s
Rust check clippy -p encointer-client-notee (x86_64-unknown-linux-gnu)	6m 32s
test_bootstrap_demo_community.sh	4m 28s
test_bot_community.sh	4m 46s
test_register_business.sh	2m 5s
Draft Release	0s
Publish Runtimes	0s
	1h 32m 15s

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