Switched references of App veyor to azure pipelines in the contributing CI section
- Related to #22829 #22760 #22690 
- [X] tests added / passed
- [X] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23311?src=pr&el=h1) Report
> Merging [#23311](https://codecov.io/gh/pandas-dev/pandas/pull/23311?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/1c26375c0743a2cbdcfe14a62ad10806001cbee8?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/23311/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/23311?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #23311   +/-   ##
=======================================
  Coverage   92.22%   92.22%           
=======================================
  Files         169      169           
  Lines       50911    50911           
=======================================
  Hits        46954    46954           
  Misses       3957     3957
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.65% <ø> (ø)` | :arrow_up: |
| #single | `42.29% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23311?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23311?src=pr&el=footer). Last update [1c26375...1df1208](https://codecov.io/gh/pandas-dev/pandas/pull/23311?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks @vadakattu pls check the built docs for correctness (will take a while for this).http://pandas-docs.github.io/pandas-docs-travis/ http://pandas-docs.github.io/pandas-docs-travis/contributing.html#testing-with-continuous-integration looks good