tests: move test_parallel_copy into performance tree

[jcsp]

Problem

This test writes ~5GB of data. It is not suitable to run in parallel with all the other small tests in test_runner/regress.

via #9537

Summary of changes

• Move test_parallel_copy into the performance directory, so that it does not run in parallel with other tests

[github-actions]

7282 tests run: 6918 passed, 0 failed, 364 skipped (full report)

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Flaky tests (2)

Postgres 16

• test_physical_replication_config_mismatch_max_locks_per_transaction: release-arm64

Postgres 15

• test_scrubber_physical_gc_ancestors[2]: release-arm64

Code coverage* (full report)

• functions: 32.7% (8043 of 24618 functions)
• lines: 47.8% (66823 of 139908 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
a750e2a at 2025-01-10T13:56:07.173Z :recycle:}