ARROW-12991: [CI] Migrate Travis-CI ARM job to "arm64-graviton2" arch
ARROW-12991: [CI] Migrate Travis-CI ARM job to "arm64-graviton2" arch

Closes #10478 from pitrou/ARROW-12991-arm64-graviton2

Lead-authored-by: Sutou Kouhei <73218711cdd5d5c30ac66da3cc4d9d9204caf34b@clear-code.com>
Co-authored-by: Antoine Pitrou <9359a4d812173b65a3a0094cd86363e79731a3c2@python.org>
Signed-off-by: Sutou Kouhei <73218711cdd5d5c30ac66da3cc4d9d9204caf34b@clear-code.com>

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