fix: clean up semaphore if thread spawn fails

When std.Thread.spawn fails in the install() function, the semaphore
that was already initialized needs to be cleaned up to prevent a
resource leak. The C++ Bun::Semaphore object allocated by init()
would otherwise never be destroyed.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/bun.js/event_loop/RuntimeInspector.zig

@@ -160,6 +160,8 @@ const posix = if (Environment.isPosix) struct {
             .stack_size = 512 * 1024,
         }, signalInspectorThread, .{}) catch |err| {
             log("thread spawn failed: {s}", .{@errorName(err)});
+            if (semaphore) |sem| sem.deinit();
+            semaphore = null;
             return false;
         };