Respect ARROW_TEST_DATA in apache-avro tests

[tustvold]

Which issue does this PR close?

Closes #.

Rationale for this change

This breaks the verify-release-candidate script

What changes are included in this PR?

Are there any user-facing changes?

[tustvold]

Taking the liberty of merging this as it is blocking the release

[alamb]

For the record, I hit this when trying to verify the release candidate

./dev/release/verify-release-candidate.sh 48.0.0 1

which results in

running 4 tests
test reader::header::test::test_header_decode ... ok
test reader::test::test_mux ... FAILED
test reader::header::test::test_header ... FAILED
test schema::tests::test_deserialize ... ok

failures:

---- reader::test::test_mux stdout ----
thread 'reader::test::test_mux' panicked at arrow-avro/src/reader/mod.rs:84:75:
called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

---- reader::header::test::test_header stdout ----
thread 'reader::header::test::test_header' panicked at arrow-avro/src/reader/header.rs:263:37:
called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }


failures:
    reader::header::test::test_header
    reader::test::test_mux

test result: FAILED. 2 passed; 2 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

error: test failed, to rerun pass `-p arrow-avro --lib`