[management] fix a flake in account_test (#6811)

## Describe your changes
In
"TestDefaultAccountManager_UpdateAccountSettings_NetworkRangePreserved",
in the beginning of the test, during account creation a random /16
subnet from 10.64.0./10 network is used. Later in the test a new range
(10.99.0.0/16) is assigned to the account, but it's one of the possible
subnets used during account creation, which sometimes leads to a
collision and failed test.
Using a network outside of the range of networks used during account
creation fixes the issue.

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functionality behavior, CLI / service flags, or introduce a new feature
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issue / Slack thread in the description). See
[CONTRIBUTING.md](https://github.com/netbirdio/netbird/blob/main/CONTRIBUTING.md#discuss-changes-with-the-netbird-team-first).

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<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Tests**
* Updated account network range test coverage to verify peer IP
reallocation with a distinct network range.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Signed-off-by: Dmitri Dolguikh <dmitri.external@netbird.io>

management/server/account_test.go

@@ -4269,7 +4269,7 @@ func TestDefaultAccountManager_UpdateAccountSettings_NetworkRangePreserved(t *te
 	}
 
 	// Sanity: an actually different range still triggers reallocation.
-	newRange := netip.MustParsePrefix("100.99.0.0/16")
+	newRange := netip.MustParsePrefix("100.60.0.0/16")
 	_, err = manager.UpdateAccountSettings(ctx, account.Id, userID, &types.Settings{
 		PeerLoginExpirationEnabled: true,
 		PeerLoginExpiration:        types.DefaultPeerLoginExpiration,