fix: build script new line at eof (#3353)

When generating the build script, it will
fail `cargo fmt -- --check` because it is
missing a new line at the end of the file.

sqlx-cli/src/migrate.rs

@@ -474,7 +474,8 @@ pub fn build_script(migration_source: &str, force: bool) -> anyhow::Result<()> {
 fn main() {{
     // trigger recompilation when a new migration is added
     println!("cargo:rerun-if-changed={migration_source}");
-}}"#,
+}}
+"#,
     );
 
     fs::write("build.rs", contents)?;