Ignore zero sized cluster size in pageserver feedback.

[arssher]

To take into account that non zero shards send 0 size. Generally we should make reporting sharding aware, but for now this will avoid breaking size limit after https://github.com/neondatabase/neon/pull/6567

[github-actions[bot]]

2376 tests run: 2264 passed, 0 failed, 112 skipped (full report)

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Flaky tests (4)

Postgres 15

• test_gc_cutoff: release
• test_emergency_mode: release

Postgres 14

• test_gc_cutoff: debug
• test_empty_tenant_size: debug

Code coverage (full report)

• functions: 54.4% (11219 of 20608 functions)
• lines: 81.5% (63284 of 77645 lines)

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_{The comment gets automatically updated with the latest test results
6d71a4fd3158e37f21dde31eeff69866f404cc03 at 2024-02-01T16:45:05.216Z :recycle:}

[petuhovskiy]

Superseded by #7100