fix(clamav): raise WRITE_TIMEOUT_SECONDS past the scan timeout

[netomi]

Summary

Staging counterpart of #13800 (aws-production).

• clamav-rest (EclipseFdn/clamav-rest-new) defaults WRITE_TIMEOUT_SECONDS to 300s and we never override it in any values file on this branch. Go's http.Server.WriteTimeout is reset when the request's headers are read and bounds the entire handler-to-response-write duration, so for any scan slower than 300s the server severs the connection well before SCAN_TIMEOUT_MINUTES elapses.
• The scan keeps running after the connection is cut, but its result is written to a connection nobody is listening on anymore — the calling openvsx server sees a bare Read timed out instead of the scan verdict, and ExtensionScanCompletionService marks the scan group ERRORED even though clamav-rest's own logs show a clean, completed scan.
• Fix: set WRITE_TIMEOUT_SECONDS above SCAN_TIMEOUT_MINUTES * 60 everywhere clamav.env is defined on this branch — base values.yaml and values-aws-staging.yaml (both currently SCAN_TIMEOUT_MINUTES: 5). values-staging.yaml/values-test.yaml don't override env, so they inherit the base fix.

Test plan

• Deploy to staging and publish an extension whose scan runs past 5 minutes; confirm the scan result now lands rather than erroring out.

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