id,node_id,number,title,user,state,locked,assignee,milestone,comments,created_at,updated_at,closed_at,author_association,active_lock_reason,draft,pull_request,body,reactions,performed_via_github_app,state_reason,repo,type
2215113392,PR_kwDOAMm_X85rJ3wR,8889,Add typing to test_plot.py,14371165,closed,0,,,0,2024-03-29T10:49:39Z,2024-04-05T16:42:27Z,2024-04-05T16:42:27Z,MEMBER,,0,pydata/xarray/pulls/8889,Enforce typing on all tests in `test_plot.py` and add the remaining type hints.,"{""url"": ""https://api.github.com/repos/pydata/xarray/issues/8889/reactions"", ""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,,13221727,pull
2215603817,I_kwDOAMm_X86ED25p,8892,ffill's tolerance argument can be strings,14371165,open,0,,,1,2024-03-29T15:49:40Z,2024-04-02T01:50:34Z,,MEMBER,,,,"### What happened?

`ffill`, `bfill` `reindex` etc. have tolerance arguments that also supports strings. And we test for it here:

https://github.com/pydata/xarray/blob/2120808bbe45f3d4f0b6a01cd43bac4df4039092/xarray/tests/test_groupby.py#L2016-L2025

But our typing assumes it's floats only:
https://github.com/pydata/xarray/blob/2120808bbe45f3d4f0b6a01cd43bac4df4039092/xarray/core/resample.py#L69-L94

### What did you expect to happen?

Since our pytests pass, mypy should pass as well.

### Minimal Complete Verifiable Example

```python
import numpy as np
import pandas as pd

import xarray as xr

# https://github.com/pydata/xarray/blob/2120808bbe45f3d4f0b6a01cd43bac4df4039092/xarray/tests/test_groupby.py#L2016
# Test tolerance keyword for upsample methods bfill, pad, nearest
times = pd.date_range(""2000-01-01"", freq=""1D"", periods=2)
times_upsampled = pd.date_range(""2000-01-01"", freq=""6h"", periods=5)
array = xr.DataArray(np.arange(2), [(""time"", times)])

# Forward fill
actual = array.resample(time=""6h"").ffill(tolerance=""12h"")
expected = xr.DataArray([0.0, 0.0, 0.0, np.nan, 1.0], [(""time"", times_upsampled)])
xr.testing.assert_identical(expected, actual)

```

### Environment
master
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2215324218,PR_kwDOAMm_X85rKmW7,8890,Add typing to test_groupby.py,14371165,closed,0,,,1,2024-03-29T13:13:59Z,2024-03-29T16:38:17Z,2024-03-29T16:38:16Z,MEMBER,,0,pydata/xarray/pulls/8890,Enforce typing on all tests in `test_groupby.py` and add the remaining type hints.,"{""url"": ""https://api.github.com/repos/pydata/xarray/issues/8890/reactions"", ""total_count"": 1, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 1, ""rocket"": 0, ""eyes"": 0}",,,13221727,pull