Bump github.com/attestantio/go-eth2-client from 0.19.8 to 0.21.3

[dependabot[bot]]

Bumps github.com/attestantio/go-eth2-client from 0.19.8 to 0.21.3.

Changelog

Sourced from github.com/attestantio/go-eth2-client's changelog.

0.21.3:

• relax requirement for proposals to use the graffiti we request

0.21.2:

• fuzz testing fixes

0.21.1:

• fix potential crash when unmarshaling Gwei values
• add WithReducedMemoryUsage() option for http service
• more consistent tracing attributes and codes

0.21.0:

• use v3 of the endpoint to obtain proposals
• add bounds checking for ValidatorState

0.20.0:

• allow delayed start of client, enabling the service even if the underlying beacon node is not ready
• add IsActive() and IsSynced() methods to understand the status of the service
• update multi clients to be aware of delayed start, only using clients that are synced
• use standard errors for common function issues
• add ProposerIndex() to VersionedSignedProposal
• add name to multi clients to differentiate multiple instances
• fully parse provided client URLs, allowing pass through of username, password, etc.

0.19.10:

• add proposer_slashing and attester_slashing events
• add bls_to_execution_change event

Commits

• be2c8f5 Remove proposal checks for graffiti.
• eb48c85 Make default user agent constant.
• cf3821c Merge pull request #130 from attestantio/linting
• b39e780 Linting and workflows.
• 48c181e Merge pull request #126 from infosecual/json-unmarshall-panic-fix
• eb1ba1e moved tests into separate files, renamed
• 0d39cba renamed new testing files
• e8c9701 added test for BlobIndexUnmarshalJSON
• c1a8ddd added tests for WithdrawalIndexUnmarshalJSON
• 7e731f7 added tests for ParticipationFlagsUnmarshalJSON
• Additional commits viewable in compare view

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