fix(cpu-template-helper): Handle a new line correctly to display error

`displaydoc::Display` doesn't recognize `\n` as a new line in doc
string:
```
Difference detected between source and target: \n{
  "name": "kernel_version",
  "prev": "5.10.215-203.850.amzn2.x86_64",
  "curr": "6.1.84-99.169.amzn2023.x86_64"
}
```
Also, it doesn't support multi-line string unless we use `/** */` style
doc, however the doc style is denied by our format check.

Signed-off-by: Takahiro Itazuri <[email protected]>

Author: zulinx86

src/cpu-template-helper/src/fingerprint/compare.rs

@@ -7,7 +7,7 @@ use crate::fingerprint::{Fingerprint, FingerprintField};
 
 #[derive(Debug, thiserror::Error, displaydoc::Display)]
 pub enum FingerprintCompareError {
-    /// Difference detected between source and target:\n{0}
+    /// Difference detected between source and target: {0}
     DiffDetected(String),
     /// Failed to serialize/deserialize JSON: {0}
     Serde(#[from] serde_json::Error),
@@ -85,7 +85,10 @@ pub fn compare(
     if results.is_empty() {
         Ok(())
     } else {
-        Err(FingerprintCompareError::DiffDetected(results.join("\n")))
+        Err(FingerprintCompareError::DiffDetected(format!(
+            "\n{}",
+            results.join("\n")
+        )))
     }
 }
 
@@ -132,7 +135,7 @@ mod tests {
             Err(FingerprintCompareError::DiffDetected(err)) => {
                 assert_eq!(
                     err,
-                    "{\
+                    "\n{\
                     \n  \"name\": \"kernel_version\",\
                     \n  \"prev\": \"sample_kernel_version\",\
                     \n  \"curr\": \"different_kernel_version\"\

src/cpu-template-helper/src/main.rs

@@ -190,14 +190,14 @@ fn run(cli: Cli) -> Result<(), HelperError> {
     Ok(())
 }
 
-fn main() {
+fn main() -> std::process::ExitCode {
     let cli = Cli::parse();
     let result = run(cli);
     if let Err(e) = result {
         eprintln!("{}", e);
-        std::process::exit(1);
+        std::process::ExitCode::FAILURE
     } else {
-        std::process::exit(0);
+        std::process::ExitCode::SUCCESS
     }
 }