Allow warnings in examples compilation (#3020)

## Motivation and Context
** needs backport **

Allow warnings in examples compilation

## Description
<!--- Describe your changes in detail -->

## Testing
Verified that `RUSTFLAGS=""` works as expected.

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Author: rcoh

tools/ci-scripts/check-aws-sdk-examples

@@ -13,7 +13,7 @@ cd aws-sdk/examples
 for example in *; do
     echo -e "${C_YELLOW}Checking examples/${example}...${C_RESET}"
     pushd "${example}" &>/dev/null
-    cargo check
+    RUSTFLAGS="" cargo check
     cargo clean
     popd &>/dev/null
 done