Update smriprep requirement from ~=0.13.1 to ~=0.15.0 (#395)

* Update smriprep requirement from ~=0.13.1 to ~=0.15.0

Updates the requirements on [smriprep](https://github.com/nipreps/smriprep) to permit the latest version.
- [Release notes](https://github.com/nipreps/smriprep/releases)
- [Changelog](https://github.com/nipreps/smriprep/blob/master/CHANGES.rst)
- [Commits](nipreps/smriprep@0.13.1...0.15.0)

---
updated-dependencies:
- dependency-name: smriprep
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

* Update pyproject.toml

---------

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Taylor Salo <[email protected]>

pyproject.toml

@@ -35,7 +35,7 @@ dependencies = [
     "requests",
     "sdcflows ~= 2.8.0",
     "sentry-sdk >= 0.6.9",
-    "smriprep ~= 0.13.1",
+    "smriprep ~= 0.15.0",
     "templateflow >= 23.0.0",
     "toml",
 
@@ -52,6 +52,7 @@ NiPreps = "https://www.nipreps.org/"
 [project.optional-dependencies]
 doc = [
     "doctest-ignore-unicode",
+    "lxml_html_clean",
     "m2r",
     "mistune < 4",  # just temporary until m2r addresses this issue
     "nbsphinx",