DOC: Not pushing the docs to github pages in PRs
In #24292 we made the doc build fail when there is a failure. But in PR builds, pushing to github pages is expected to fail, so the build job is failing for every PR now. Pushing docs to github pages only for `master` builds in this PR (we still build the docs, to make sure it doesn't fail).
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24316?src=pr&el=h1) Report
> Merging [#24316](https://codecov.io/gh/pandas-dev/pandas/pull/24316?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/41780e5af910b5fab072bdc6d6993c04b8f0718b?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/24316/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24316?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #24316   +/-   ##
=======================================
  Coverage   92.28%   92.28%           
=======================================
  Files         162      162           
  Lines       51831    51831           
=======================================
  Hits        47831    47831           
  Misses       4000     4000
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.68% <ø> (ø)` | :arrow_up: |
| #single | `43.01% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24316?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/24316?src=pr&el=footer). Last update [41780e5...9d33201](https://codecov.io/gh/pandas-dev/pandas/pull/24316?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24316?src=pr&el=h1) Report
> Merging [#24316](https://codecov.io/gh/pandas-dev/pandas/pull/24316?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/41780e5af910b5fab072bdc6d6993c04b8f0718b?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/24316/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24316?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #24316   +/-   ##
=======================================
  Coverage   92.28%   92.28%           
=======================================
  Files         162      162           
  Lines       51831    51831           
=======================================
  Hits        47831    47831           
  Misses       4000     4000
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.68% <ø> (ø)` | :arrow_up: |
| #single | `43.01% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24316?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/24316?src=pr&el=footer). Last update [41780e5...75f1434](https://codecov.io/gh/pandas-dev/pandas/pull/24316?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks