[Doc]: fix typos in Python comments (#24294)

Signed-off-by: Didier Durand <durand.didier@gmail.com>
Co-authored-by: Wentao Ye <44945378+yewentao256@users.noreply.github.com>

vllm/envs.py

@@ -1064,7 +1064,7 @@ environment_variables: dict[str, Callable[[], Any]] = {
     # vllm should use flashinfer fused allreduce. The variable should be a
     # JSON with the following format:
     #     { <world size>: <max size in mb> }
-    # Unspecified world sizes will fallback to
+    # Unspecified world sizes will fall back to
     #     { 2: 64, 4: 1, <everything else>: 0.5 }
     "VLLM_FLASHINFER_ALLREDUCE_FUSION_THRESHOLDS_MB":
     lambda: json.loads(os.getenv(