docs: update 2.35 latest release to v2.35.3 (#27511)

Updates the release calendar in `docs/install/releases/index.md` so the
2.35 mainline row points at the latest patch release `v2.35.3` instead
of `v2.35.2`.

> [!NOTE]
> This PR was generated by Coder Agents on behalf of @mtojek.

---------

Co-authored-by: Nick Vigilante <nickvigilante@users.noreply.github.com>

docs/install/kubernetes.md

@@ -135,7 +135,7 @@ We support two release channels: mainline and stable - read the
     helm install coder coder-v2/coder \
         --namespace coder \
         --values values.yaml \
-        --version 2.34.0
+        --version 2.35.3
     ```
 
   - **OCI Registry**
@@ -146,7 +146,7 @@ We support two release channels: mainline and stable - read the
     helm install coder oci://ghcr.io/coder/chart/coder \
         --namespace coder \
         --values values.yaml \
-        --version 2.34.0
+        --version 2.35.3
     ```
 
 - **Stable** Coder release:

docs/install/rancher.md

@@ -134,7 +134,7 @@ kubectl create secret generic coder-db-url -n coder \
 
 1. Select a Coder version:
 
-   - **Mainline**: `2.35.2`
+   - **Mainline**: `2.35.3`
    - **Stable**: `2.34.6`
 
    Learn more about release channels in the [Releases documentation](./releases/index.md).