chore: Update Mainnet IC revisions canisters file (#11199)

Update mainnet system canisters revisions file to include the latest
WASM version released on the mainnet.

This PR is created automatically using
[`mainnet_revisions.py`](https://github.com/dfinity/ic/blob/master/ci/src/mainnet_revisions/mainnet_revisions.py)

Co-authored-by: CI Automation <infra+github-automation@dfinity.org>

Author: pr-creation-bot-dfinity-ic[bot]

mainnet-canister-revisions.json

@@ -84,8 +84,8 @@
     "sha256": "b443df3315902404b142d60f3cfd2f580181683310f6e6321b52de297deffcda"
   },
   "internet_identity_backend": {
-    "sha256": "fd51df0366bff3e3dae13eadc3baa5f228397dfc49a7ee3b1e7c6683908625ea",
-    "tag": "release-2026-08-14"
+    "sha256": "e9f05b68d6817c7d9bcfbfb8cdde0d816e4d592052b340b42dab1969e867a0a1",
+    "tag": "release-2026-08-18"
   },
   "internet_identity_frontend": {
     "sha256": "ef4f04868f0c32227989cb7ac529bcb16e6bd7fb9874fb21779c020a6282b343",