test: fix test_qdisc_tbf regex with iproute2 v6.15

test: fix test_qdisc_tbf regex with iproute2 v6.15

iproute2 v6.15 fixed some rounding errors in the reported stats:

https://git.kernel.org/pub/scm/network/iproute2/iproute2.git/commit/?id=d947f365602b30657d1b797e7464000d0ab88d5a

so the current regex doesn't work anymore. Fix it to check for both
old and new values.

systemd-networkd-tests.py[523]: FAIL: test_qdisc_tbf (__main__.NetworkdTCTests.test_qdisc_tbf)
systemd-networkd-tests.py[523]: ----------------------------------------------------------------------
systemd-networkd-tests.py[523]: Traceback (most recent call last):
systemd-networkd-tests.py[523]:   File "/usr/lib/systemd/tests/testdata/test-network/systemd-networkd-tests.py", line 5402, in test_qdisc_tbf
systemd-networkd-tests.py[523]:     self.assertRegex(output, 'rate 1Gbit burst 5000b peakrate 100Gbit minburst 987500b lat 70(.0)?ms')
systemd-networkd-tests.py[523]:     ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
systemd-networkd-tests.py[523]: AssertionError: Regex didn't match: 'rate 1Gbit burst 5000b peakrate 100Gbit minburst 987500b lat 70(.0)?ms' not found in 'qdisc tbf 35: root refcnt 2 rate 1Gbit burst 5000b peakrate 100Gbit minburst 999200b lat 70ms \nqdisc pfifo 37: parent 35: limit 100000p'

(cherry picked from commit f9a85b74903f5588d08f54ea7d9b53edc639b824)