chore: bump gitpython from 3.1.54 to 3.1.57 in /docs (#2600)

Bumps the transitive gitpython pin in the docs toolchain from 3.1.54 to 3.1.57, closing 4 open GHSA advisories. Reviewed and approved by @phipag. Review performed by Claude.

Author: dependabot[bot]

docs/requirements.txt

@@ -22,9 +22,9 @@ gitdb==4.0.12 \
     --hash=sha256:5ef71f855d191a3326fcfbc0d5da835f26b13fbcba60c32c21091c349ffdb571 \
     --hash=sha256:67073e15955400952c6565cc3e707c554a4eea2e428946f7a4c162fab9bd9bcf
     # via gitpython
-gitpython==3.1.54 \
-    --hash=sha256:53f2085e24a2cda300eed7c3fc5f1559ae289634b725e98acaf4791940247aa0 \
-    --hash=sha256:b90d7b3d9bc0238681d24369130826f0dcdb0ceaa45db67cf1d4ffa4c302dedf
+gitpython==3.1.57 \
+    --hash=sha256:4ccf7d73c10f5c9e76043fbb2675ac5a1b3ff5b41e648f56bcbed5f63792ecaf \
+    --hash=sha256:c493ec57c0ef6b19743798b6a5af859c71814b524e7e6f97baa2f8e658961488
     # via mkdocs-git-revision-date-plugin
 hjson==3.1.0 \
     --hash=sha256:55af475a27cf83a7969c808399d7bccdec8fb836a07ddbd574587593b9cdcf75 \