Bump github.com/attestantio/go-eth2-client from 0.21.1 to 0.21.9

[dependabot]

Bumps github.com/attestantio/go-eth2-client from 0.21.1 to 0.21.9.

Changelog

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

0.21.9:

• enable custom timeouts for POSTs

0.21.8:

• remove Lodestar proposals workaround
• add client headers for events stream

0.21.7:

• use POST for specific validator and validator balance information

0.21.6:

• use SSZ on a per-call basis

0.21.5:

• ensure POST bodies are logged as JSON

0.21.4:

• additional nil checks
• allow non-mainnet configurations

0.21.3:

• relax requirement for proposals to use the graffiti we request

0.21.2:

• fuzz testing fixes

Commits

• 633b784 Formatting.
• 512fdce Bump version.
• 2450464 Enable per-request timeout for POSTs.
• 22abb36 Enable per-request timeout for POSTs.
• 166b693 Release 0.21.8
• eff49f7 Use xxxxx rather than *** to mask sensitive data in URLs.
• 73945ba Set appropriate Accept header for events.
• 0138132 Add client headers for events stream.
• 5f15ea2 Remove unused code.
• a947ded Merge pull request #148 from nflaig/patch-1
• Additional commits viewable in compare view

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