DeprecationWarning in matplotlib trips linux-cp3.11-mini-req-optional-deps

While working on a few PRs of mine I noticed that [linux-cp3.11-mini-req-optional-deps](https://github.com/scikit-image/scikit-image/blob/f874e612be992a8463da98f9c7ad37a8f79a6dbe/.github/workflows/test-linux.yaml#L52-L56) consistently fails during pytests test collection. This [failure can also be reproduced on `main`](https://github.com/scikit-image/scikit-image/actions/runs/20401045924/job/59099960544#step:9:169). 

Here's a the error [message from the test collection](https://github.com/scikit-image/scikit-image/actions/runs/20401045924/job/59099960544#step:9:169):

<details><summary>Details</summary>

```
/opt/hostedtoolcache/Python/3.11.14/x64/lib/python3.11/site-packages/matplotlib/_fontconfig_pattern.py:88: in parse_fontconfig_pattern
    parse = parser.parseString(pattern)
        parser     = {{{[Re:('([^\\\-:,]|(\\[\\\-:,]))*') [{Suppress:(',') Re:('([^\\\-:,]|(\\[\\\-:,]))*')}]...] ['-' {Re:('([0-9]+\.?[0-9...[^\\=_:,]|(\\[\\=_:,]))*') [{Suppress:(',') Re:('([^\\=_:,]|(\\[\\=_:,]))*')}]...} | Re:('[a-z]+')})}]...} end of text}
        pattern    = 'sans:bold'
/opt/hostedtoolcache/Python/3.11.14/x64/lib/python3.11/site-packages/pyparsing/util.py:434: in _inner
    warnings.warn(
E   DeprecationWarning: 'parseString' deprecated - use 'parse_string'
```

</details> 

I'm not sure what's caused this to appear. The [same workflow on `main` passed 9 days ago](https://github.com/scikit-image/scikit-image/actions/runs/20401045924/job/58623404675). 

It seems that linux-cp3.11-mini-req-eager-import is unaffected by this. Probably because that one doesn't install matplotlib.

[]