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GH-26209: [Ruby] Add support for Ruby 2.5 (#33602)

# Which issue does this PR close?

Closes #26209

# Rationale for this change

Ruby 2.5 was EOL but Ubuntu 18.04 still uses Ruby 2.5. Note that Ubuntu 18.04 will reach EOL on 2023-04.

# What changes are included in this PR?

Ruby 2.5 compatible implementation and tests.

# Are these changes tested?

Yes

# Are there any user-facing changes?

No.

* Closes: #26209

Authored-by: Sutou Kouhei <kou@clear-code.com>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>