build(deps): bump sphinxcontrib-serializinghtml in /tools/base

Bumps [sphinxcontrib-serializinghtml](https://github.com/sphinx-doc/sphinxcontrib-serializinghtml) from 1.1.10 to 2.0.0.
- [Release notes](https://github.com/sphinx-doc/sphinxcontrib-serializinghtml/releases)
- [Changelog](https://github.com/sphinx-doc/sphinxcontrib-serializinghtml/blob/master/CHANGES.rst)
- [Commits](sphinx-doc/sphinxcontrib-serializinghtml@1.1.10...2.0.0)

---
updated-dependencies:
- dependency-name: sphinxcontrib-serializinghtml
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

tools/base/requirements.txt

@@ -1309,9 +1309,9 @@ sphinxcontrib-qthelp==1.0.8 \
     # via
     #   -r requirements.in
     #   sphinx
-sphinxcontrib-serializinghtml==1.1.10 \
-    --hash=sha256:326369b8df80a7d2d8d7f99aa5ac577f51ea51556ed974e7716cfd4fca3f6cb7 \
-    --hash=sha256:93f3f5dc458b91b192fe10c397e324f262cf163d79f3282c158e8436a2c4511f
+sphinxcontrib-serializinghtml==2.0.0 \
+    --hash=sha256:6e2cb0eef194e10c27ec0023bfeb25badbbb5868244cf5bc5bdc04e4464bf331 \
+    --hash=sha256:e9d912827f872c029017a53f0ef2180b327c3f7fd23c87229f7a8e8b70031d4d
     # via
     #   -r requirements.in
     #   envoy-docs-sphinx-runner