Make canary use the same MSRV and nightly with smithy-rs (#1192)

**DO NOT MERGE THIS WHILE A RELEASE IS ONGOING**

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.github/workflows/canary.yaml

@@ -7,8 +7,8 @@ on:
     branches:
       - "canary*"
 env:
-  tool_rust_version: 1.76.0
-  rust_nightly_version: nightly-2024-02-07
+  tool_rust_version: 1.78.0
+  rust_nightly_version: nightly-2024-03-15
 
 jobs:
   generate-canary-matrix:
@@ -54,7 +54,6 @@ jobs:
       # Use the matrix generated by the previous job
       matrix: ${{ fromJson(needs.generate-canary-matrix.outputs.matrix) }}
     steps:
-      - uses: actions/checkout@v4
       - uses: actions/checkout@v4
         with:
           repository: awslabs/smithy-rs