test: fix replacing .exe only once

On non-Windows platform the redacted string became something like below,
which was valid but didn't make sense:

```
[EXE]/[EXE]U[EXE]s[EXE]e[EXE]r[EXE]s[EXE]/[EXE]w[EXE]h[EXE]l[EXE]o[EXE]/[EXE]d[EXE]e[EXE]v[EXE]/[EXE]r[EXE]u[EXE]s[EXE]t[EXE]/[EXE]b[EXE]u[EXE]i[EXE]l[EXE]d[EXE]/[EXE]a[EXE]a[EXE]r[EXE]c[EXE]h[EXE]6[EXE]4[EXE]-[EXE]a[EXE]p[EXE]p[EXE]l[EXE]e[EXE]-[EXE]d[EXE]a[EXE]r[EXE]w[EXE]i[EXE]n[EXE]/[EXE]s[EXE]t[EXE]a[EXE]g[EXE]e[EXE]2[EXE]-[EXE]t[EXE]o[EXE]o[EXE]l[EXE]s[EXE]/[EXE]a[EXE]a[EXE]r[EXE]c[EXE]h[EXE]6[EXE]4[EXE]-[EXE]a[EXE]p[EXE]p[EXE]l[EXE]e[EXE]-[EXE]d[EXE]a[EXE]r[EXE]w[EXE]i[EXE]n[EXE]/[EXE]r[EXE]e[EXE]l[EXE]e[EXE]a[EXE]s[EXE]e[EXE]/[EXE]c[EXE]a[EXE]r[EXE]g[EXE]o[EXE]
```

Here we simply remove the extension and append `[EXE]` at the end.

tests/testsuite/test.rs

@@ -3888,12 +3888,15 @@ fn cargo_test_env() {
         .file("src/lib.rs", &src)
         .build();
 
-    let cargo = cargo_exe()
-        .canonicalize()
-        .unwrap()
-        .to_str()
-        .unwrap()
-        .replace(std::env::consts::EXE_SUFFIX, "[EXE]");
+    let cargo = format!(
+        "{}[EXE]",
+        cargo_exe()
+            .canonicalize()
+            .unwrap()
+            .with_extension("")
+            .to_str()
+            .unwrap()
+    );
     p.cargo("test --lib -- --nocapture")
         .with_stderr_contains(cargo)
         .with_stdout_data(str![[r#"
@@ -3908,10 +3911,7 @@ test env_test ... ok
         .unwrap()
         .canonicalize()
         .unwrap();
-    let stderr_rustc = rustc
-        .to_str()
-        .unwrap()
-        .replace(std::env::consts::EXE_SUFFIX, "[EXE]");
+    let stderr_rustc = format!("{}[EXE]", rustc.with_extension("").to_str().unwrap());
     p.cargo("test --lib -- --nocapture")
         // we use rustc since $CARGO is only used if it points to a path that exists
         .env(cargo::CARGO_ENV, rustc)