Fix v20 tag SHA

[shlomi-noach]

As part of https://github.com/vitessio/vitess/issues/16010, see also:

• https://github.com/vitessio/vitess/pull/16146
• https://github.com/vitessio/vitess/pull/16145
• https://github.com/vitessio/vitess/pull/16144

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