Fix function call for release testable

[ChristineTChen]

What does this PR do?

get_pr() no longer takes a repo argument.

https://github.com/DataDog/integrations-core/blob/master/datadog_checks_dev/datadog_checks/dev/tooling/github.py#L55

Motivation

ddev release testable would get an unexpected keyword argument:

± |master {5} ✓| → ddev release testable --since 6.16
Branch `6.16.x` will be compared to `origin/master`.
Getting diff... failed!
Local branch `6.16.x` might not exist, trying `origin/6.16.x`... success!
Traceback (most recent call last):
  File "/usr/local/bin/ddev", line 11, in <module>
    load_entry_point('datadog-checks-dev', 'console_scripts', 'ddev')()
  File "/usr/local/lib/python3.7/site-packages/click/core.py", line 764, in __call__
    return self.main(*args, **kwargs)
  File "/usr/local/lib/python3.7/site-packages/click/core.py", line 717, in main
    rv = self.invoke(ctx)
  File "/usr/local/lib/python3.7/site-packages/click/core.py", line 1137, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/local/lib/python3.7/site-packages/click/core.py", line 1137, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/local/lib/python3.7/site-packages/click/core.py", line 956, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/usr/local/lib/python3.7/site-packages/click/core.py", line 555, in invoke
    return callback(*args, **kwargs)
  File "/usr/local/lib/python3.7/site-packages/click/decorators.py", line 17, in new_func
    return f(get_current_context(), *args, **kwargs)
  File "/Users/christine.chen/dev/integrations-core/datadog_checks_dev/datadog_checks/dev/tooling/commands/release/testable.py", line 183, in testable
    api_response = get_pr(commit_id, user_config, repo=repo, raw=True)
TypeError: get_pr() got an unexpected keyword argument 'repo'

Additional Notes

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• PR title must be written as a CHANGELOG entry (see why)
• Files changes must correspond to the primary purpose of the PR as described in the title (small unrelated changes should have their own PR)
• PR must have changelog/ and integration/ labels attached

[codecov]

Codecov Report

Merging #5432 into master will decrease coverage by 2.57%.
The diff coverage is n/a.

Impacted Files	Coverage Δ
vertica/tests/metrics.py
clickhouse/datadog_checks/clickhouse/utils.py
riakcs/datadog_checks/riakcs/riakcs.py
mesos_slave/tests/conftest.py
linkerd/datadog_checks/linkerd/linkerd.py
...oller/datadog_checks/openstack_controller/utils.py
istio/tests/test_e2e.py
gitlab_runner/tests/test_integration.py
disk/datadog_checks/disk/__init__.py
...hecks/openstack_controller/openstack_controller.py
... and 849 more