[deps]: Update rust Docker tag to v1.81 (#948)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| rust | stage | minor | `1.76` -> `1.81` |
| rust | final | minor | `1.76` -> `1.81` |

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crates/bws/Dockerfile

@@ -1,7 +1,7 @@
 ###############################################
 #                 Build stage                 #
 ###############################################
-FROM --platform=$BUILDPLATFORM rust:1.76 AS build
+FROM --platform=$BUILDPLATFORM rust:1.81 AS build
 
 # Docker buildx supplies the value for this arg
 ARG TARGETPLATFORM

crates/memory-testing/Dockerfile

@@ -1,7 +1,7 @@
 ###############################################
 #                 Build stage                 #
 ###############################################
-FROM rust:1.76 AS build
+FROM rust:1.81 AS build
 
 WORKDIR /app