fix(dev-infra): incorrect token sanitization when no token is specified (#37489)

We recently moved over the git client from the merge script to the
common dev-infra utils. This made specifying a token optional, but
it looks like the logic for sanitizing messages doesn't account
for that, and we currently add `<TOKEN>` between every message
character. e.g.

```
Executing: git <TOKEN>g<TOKEN>i<TOKEN>t<TOKEN>
<TOKEN>s<TOKEN>t<TOKEN>a<TOKEN>t<TOKEN>u<TOKEN>s<TOKEN>
```

PR Close #37489

dev-infra/utils/shelljs.ts

@@ -8,7 +8,10 @@
 
 import {exec as _exec, ExecOptions, ShellString} from 'shelljs';
 
-/* Run an exec command as silent. */
-export function exec(cmd: string, opts?: ExecOptions&{async?: false}): ShellString {
-  return _exec(cmd, {silent: true, ...opts});
+/**
+ * Runs an given command as child process. By default, child process
+ * output will not be printed.
+ */
+export function exec(cmd: string, opts?: Omit<ExecOptions, 'async'>): ShellString {
+  return _exec(cmd, {silent: true, ...opts, async: false});
 }