Style/HashSyntax: Set EnforcedShorthandSyntax to `either_consistent`

What does this MR do and why?

Examples:

# good - `foo` and `bar` values can be omitted, but they are consistent, so it's accepted
{foo: foo, bar: bar}

# bad - `bar` value can be omitted
{foo:, bar: bar}

# bad - mixed syntaxes
{foo:, bar: baz}

# good
{foo:, bar:}

# good - can't omit `baz`
{foo: foo, bar: baz}

See also gitlab-org/gitlab!161622 (merged)

Config diff rubocop --show-cops

--- before	2024-10-29 10:48:45.024558411 +0100
+++ after	2024-10-29 10:46:27.510401588 +0100
@@ -5374,7 +5374,7 @@
   - hash_rockets
   - no_mixed_keys
   - ruby19_no_mixed_keys
-  EnforcedShorthandSyntax: never
+  EnforcedShorthandSyntax: either_consistent
   SupportedShorthandSyntax:
   - always
   - never
`'`