TST: relax test tolerances for BinomTest
TST: relax test tolerances for BinomTest

These rtol values were unnecessarily tight and caused these failures
on aarch64 on the scipy-wheels CI:

```
____________________ TestBinomTest.test_two_sided_pvalues1 _____________________
[gw2] linux -- Python 3.9.2 /venv/bin/python
/venv/lib/python3.9/site-packages/scipy/stats/tests/test_morestats.py:700: in test_two_sided_pvalues1
    assert_allclose(res.pvalue, 0.979042561004596, rtol=1e-15)
E   AssertionError:
E   Not equal to tolerance rtol=1e-15, atol=0
E
E   Mismatched elements: 1 / 1 (100%)
E   Max absolute difference: 3.5005332e-13
E   Max relative difference: 3.5754658e-13
E    x: array(0.979043)
E    y: array(0.979043)

        res        = BinomTestResult(k=10079999, n=21000000, alternative='two-sided', proportion_estimate=0.4799999523809524, pvalue=0.9790425610042459)
        self       = <scipy.stats.tests.test_morestats.TestBinomTest object at 0xffff6e2bf100>

________________________ TestBinomTest.test_edge_cases _________________________
[gw2] linux -- Python 3.9.2 /venv/bin/python
/venv/lib/python3.9/site-packages/scipy/stats/tests/test_morestats.py:730: in test_edge_cases
    assert_allclose(res.pvalue, 0.999999999998212, rtol=1e-15)
E   AssertionError:
E   Not equal to tolerance rtol=1e-15, atol=0
E
E   Mismatched elements: 1 / 1 (100%)
E   Max absolute difference: 1.33226763e-15
E   Max relative difference: 1.33226763e-15
E    x: array(1.)
E    y: array(1.)

        res        = BinomTestResult(k=484, n=967, alternative='two-sided', proportion_estimate=0.500517063081696, pvalue=0.9999999999982133)
        self       = <scipy.stats.tests.test_morestats.TestBinomTest object at 0xffff6e2ce5e0>
```

matthew-brett/scipy,endolith/scipy,zerothi/scipy,vigna/scipy,Eric89GXL/scipy,grlee77/scipy,andyfaff/scipy,e-q/scipy,e-q/scipy,scipy/scipy,perimosocordiae/scipy,endolith/scipy,andyfaff/scipy,grlee77/scipy,tylerjereddy/scipy,perimosocordiae/scipy,ilayn/scipy,endolith/scipy,endolith/scipy,rgommers/scipy,matthew-brett/scipy,anntzer/scipy,scipy/scipy,perimosocordiae/scipy,endolith/scipy,ilayn/scipy,WarrenWeckesser/scipy,perimosocordiae/scipy,Stefan-Endres/scipy,mdhaber/scipy,matthew-brett/scipy,anntzer/scipy,Eric89GXL/scipy,perimosocordiae/scipy,ilayn/scipy,vigna/scipy,tylerjereddy/scipy,Eric89GXL/scipy,anntzer/scipy,scipy/scipy,mdhaber/scipy,scipy/scipy,e-q/scipy,mdhaber/scipy,grlee77/scipy,zerothi/scipy,mdhaber/scipy,matthew-brett/scipy,Stefan-Endres/scipy,WarrenWeckesser/scipy,Eric89GXL/scipy,endolith/scipy,Eric89GXL/scipy,tylerjereddy/scipy,zerothi/scipy,WarrenWeckesser/scipy,andyfaff/scipy,WarrenWeckesser/scipy,Stefan-Endres/scipy,zerothi/scipy,Stefan-Endres/scipy,vigna/scipy,ilayn/scipy,rgommers/scipy,tylerjereddy/scipy,mdhaber/scipy,WarrenWeckesser/scipy,grlee77/scipy,matthew-brett/scipy,anntzer/scipy,tylerjereddy/scipy,Eric89GXL/scipy,mdhaber/scipy,anntzer/scipy,andyfaff/scipy,rgommers/scipy,vigna/scipy,zerothi/scipy,Stefan-Endres/scipy,rgommers/scipy,perimosocordiae/scipy,andyfaff/scipy,vigna/scipy,anntzer/scipy,scipy/scipy,e-q/scipy,andyfaff/scipy,ilayn/scipy,e-q/scipy,grlee77/scipy,ilayn/scipy,Stefan-Endres/scipy,scipy/scipy,zerothi/scipy,WarrenWeckesser/scipy,rgommers/scipy