upgrade to polkadot v1.8.0 #751

Job	Run time
Build Runtimes (encointer-node-notee)	3m 49s
build-try-runtime-and-benchmarks	5m 37s
build	4m 28s
Cancel Previous Runs	2s
cargo-toml-fmt	11s
Rust check +nightly fmt --all -- --check (x86_64-unknown-linux-gnu)	26s
unit-tests	2m 25s
Rust check clippy -p encointer-client-notee (x86_64-unknown-linux-gnu)	5m 55s
test_bootstrap_demo_community.sh	18m 52s
test_bot_community.sh	7m 52s
test_register_business.sh	1m 58s
Draft Release	0s
Publish Runtimes	0s
	51m 35s

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