Upgrade upstream to v1.20.2

[ToufeeqP]

Pull Request type

Please add the labels corresponding to the type of changes your PR introduces:

• Upgrade:

Description

Upgrade polkadot-sdk to v1.20.2

Companion PRs

avail-core: PR #134
polkadot-sdk: PR #27

Testing Performed

Checklist

• I have performed a self-review of my own code.
• The tests pass successfully with cargo test.
• The code was formatted with cargo fmt.
• The code compiles with no new warnings with cargo build --release and cargo build --release --features runtime-benchmarks.
• The code has no new warnings when using cargo clippy.
• If this change affects documented features or needs new documentation, I have created a PR with a documentation update.