tox: set ignore_errors

This doesn't actually *ignore* errors, it just means we continue
running commands after one errors out instead of immediately
bailing. This avoids problems like "the tests don't run if
check-needles fails, so then the coverage reports fail because
there's no coverage.xml".

Signed-off-by: Adam Williamson <awilliam@redhat.com>

tox.ini

@@ -3,6 +3,7 @@ skipsdist = True
 envlist = py37,py38,py39,py310,py311,coverage-report
 skip_missing_interpreters = true
 [testenv]
+ignore_errors = true
 deps =
     pytest
     jsonschema
@@ -18,6 +19,7 @@ setenv =
 
 [testenv:coverage-report]
 skip_install = true
+ignore_errors = true
 deps =
     diff-cover
     pylint