tests: ospf_netns_vrf should give more time for coming up (backport #16683)

[mergify]

Test fails:

        test_func = partial(
            topotest.router_json_cmp,
            router,
            "show ip ospf vrf {0}-ospf-cust1 json".format(rname),
            expected,
        )
        _, diff = topotest.run_and_expect(test_func, None, count=10, wait=0.5)
        assertmsg = '"{}" JSON output mismatches'.format(rname)

      assert diff is None, assertmsg

E AssertionError: "r1" JSON output mismatches
E assert Generated JSON diff error report:
E
E > $->r1-ospf-cust1->areas->0.0.0.0->nbrFullAdjacentCounter: output has element with value '1' but in expected it has value '2'

/home/sharpd/frr2/tests/topotests/ospf_netns_vrf/test_ospf_netns_vrf.py:239: AssertionError

Support bundle has this data:
r1# show ip ospf vrf all neighbor
% 2024/08/28 14:55:54.763

VRF Name: r1-ospf-cust1

Neighbor ID Pri State Up Time Dead Time Address Interface RXmtL RqstL DBsmL
10.0.255.3 1 Full/DR 10.547s 39.456s 10.0.3.1 r1-eth1:10.0.3.2 0 0 0
10.0.255.2 1 Full/Backup 0.543s 38.378s 10.0.3.3 r1-eth1:10.0.3.2 1 0 0

So immediately after the test fails this test, the neighbor comes up. Let's give the test a bit more time for failure to not happen

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This is an automatic backport of pull request #16683 done by Mergify.