Bump pytest from 8.3.3 to 9.0.3 in /mjx

Bumps [pytest](https://github.com/pytest-dev/pytest) from 8.3.3 to 9.0.3.
- [Release notes](https://github.com/pytest-dev/pytest/releases)
- [Changelog](https://github.com/pytest-dev/pytest/blob/main/CHANGELOG.rst)
- [Commits](https://github.com/pytest-dev/pytest/compare/8.3.3...9.0.3)

---
updated-dependencies:
- dependency-name: pytest
  dependency-version: 9.0.3
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

mjx/requirements.txt

@@ -67,8 +67,9 @@ jaxlib==0.4.38; python_version >= '3.10' and python_version <= '3.13' and sys_pl
 pip==25.2 \
     --hash=sha256:578283f006390f85bb6282dffb876454593d637f5d1be494b5202ce4877e71f2 \
     --hash=sha256:6d67a2b4e7f14d8b31b8b52648866fa717f45a1eb70e83002f4331d07e953717
-pytest==8.3.3 \
-    --hash=sha256:a6853c7375b2663155079443d2e45de913a911a11d669df02a50814944db57b2
+pytest==9.0.3 \
+    --hash=sha256:2c5efc453d45394fdd706ade797c0a81091eccd1d6e4bccfcd476e2b8e0ab5d9 \
+    --hash=sha256:b86ada508af81d19edeb213c681b1d48246c1a91d304c6c81a427674c17eb91c
 pytest-xdist==3.6.1 \
     --hash=sha256:9ed4adfb68a016610848639bb7e02c9352d5d9f03d04809919e2dafc3be4cca7
 scipy==1.17.0; python_version >= '3.13' \