Bump snowballstemmer from 2.0.0 to 2.1.0 in /requirements (#16372)

Bumps [snowballstemmer](https://github.com/snowballstem/snowball) from 2.0.0 to 2.1.0.
- [Release notes](https://github.com/snowballstem/snowball/releases)
- [Changelog](https://github.com/snowballstem/snowball/blob/master/NEWS)
- [Commits](https://github.com/snowballstem/snowball/compare/v2.0.0...v2.1.0)

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

requirements/docs.txt

@@ -89,9 +89,9 @@ sphinxcontrib-qthelp==1.0.3 \
 sphinx-rtd-theme==0.5.1 \
     --hash=sha256:fa6bebd5ab9a73da8e102509a86f3fcc36dec04a0b52ea80e5a033b2aba00113 \
     --hash=sha256:eda689eda0c7301a80cf122dad28b1861e5605cbf455558f3775e1e8200e83a5
-snowballstemmer==2.0.0 \
-    --hash=sha256:209f257d7533fdb3cb73bdbd24f436239ca3b2fa67d56f6ff88e86be08cc5ef0 \
-    --hash=sha256:df3bac3df4c2c01363f3dd2cfa78cce2840a79b9f1c2d2de9ce8d31683992f52
+snowballstemmer==2.1.0 \
+    --hash=sha256:b51b447bea85f9968c13b650126a888aabd4cb4463fca868ec596826325dedc2 \
+    --hash=sha256:e997baa4f2e9139951b6f4c631bad912dfd3c792467e2f03d7239464af90e914
 chardet==4.0.0 \
     --hash=sha256:f864054d66fd9118f2e67044ac8981a54775ec5b67aed0441892edb553d21da5 \
     --hash=sha256:0d6f53a15db4120f2b08c94f11e7d93d2c911ee118b6b30a04ec3ee8310179fa