ci: pin valgrind to rustc 1.82 (#6998)

.github/workflows/ci.yml

@@ -283,7 +283,7 @@ jobs:
       - name: Install Rust ${{ env.rust_stable }}
         uses: dtolnay/rust-toolchain@stable
         with:
-            toolchain: ${{ env.rust_stable }}
+            toolchain: 1.82
 
       - name: Install Valgrind
         uses: taiki-e/install-action@valgrind

.github/workflows/stress-test.yml

@@ -13,7 +13,7 @@ env:
   RUSTFLAGS: -Dwarnings
   RUST_BACKTRACE: 1
   # Change to specific Rust release to pin
-  rust_stable: stable
+  rust_stable: 1.82
 
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