Bump urllib3 from 2.6.0 to 2.6.3 in /docs/requirements (mozilla#3886)

Bumps [urllib3](https://github.com/urllib3/urllib3) from 2.6.0 to 2.6.3.
- [Release notes](https://github.com/urllib3/urllib3/releases)
- [Changelog](https://github.com/urllib3/urllib3/blob/main/CHANGES.rst)
- [Commits](urllib3/urllib3@2.6.0...2.6.3)

---
updated-dependencies:
- dependency-name: urllib3
  dependency-version: 2.6.3
  dependency-type: direct:production
...

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

Author: dependabot[bot]

docs/requirements/default.in

@@ -20,4 +20,4 @@ sphinxcontrib-htmlhelp==2.1.0
 sphinxcontrib-jsmath==1.0.1
 sphinxcontrib-qthelp==2.0.0
 sphinxcontrib-serializinghtml==2.0.0
-urllib3==2.6.0
+urllib3==2.6.3

docs/requirements/default.txt

@@ -280,9 +280,9 @@ sphinxcontrib-serializinghtml==2.0.0 \
     # via
     #   -r default.in
     #   sphinx
-urllib3==2.6.0 \
-    --hash=sha256:c90f7a39f716c572c4e3e58509581ebd83f9b59cced005b7db7ad2d22b0db99f \
-    --hash=sha256:cb9bcef5a4b345d5da5d145dc3e30834f58e8018828cbc724d30b4cb7d4d49f1
+urllib3==2.6.3 \
+    --hash=sha256:1b62b6884944a57dbe321509ab94fd4d3b307075e0c2eae991ac71ee15ad38ed \
+    --hash=sha256:bf272323e553dfb2e87d9bfd225ca7b0f467b919d7bbd355436d3fd37cb0acd4
     # via
     #   -r default.in
     #   requests