docs: A comment for field filter in message .google.cloud.maintenance.api.v1.SummarizeMaintenancesRequest is changed (#8821)

* docs: A comment for field `filter` in message `.google.cloud.maintenance.api.v1.SummarizeMaintenancesRequest` is changed
chore: fix typo in API description

PiperOrigin-RevId: 845900064

Source-Link: googleapis/googleapis@6d6acd2

Source-Link: googleapis/googleapis-gen@0785330
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