When merging blob reports test ids are patched to make sure there is no
collision when merging reports that might have overlapping test ids.
However, even if you were merging reports that had no overlapping ids,
all test ids will be modified, which is an undesirable side effect.
This PR only modify test ids when the same test id has already been used
in a previous blob report.
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This change is also part of
https://github.com/microsoft/playwright/pull/30962
5708148496