Add calloop::sources=debug to default log filters (#23763)

# Objective

When setting the default log level to `trace` (e.g. with
`RUST_LOG=trace`), one of the log messages that gets enabled looks like
`[calloop] Processing events for source type ...`. This message is
logged at the trace level 1-3 times every frame, making it extremely
spammy. Although the purpose of trace-level logs is to be verbose,
logging the same unactionable thing every frame is excessive.
While normally there would be a bunch of stuff that always gets logged
every frame, the default filters provided by `LogPlugin` exclude all of
that at every log level, except for this one thing which slips through.

## Solution

Add the offending module to the default filters.

## Testing

Manually tested with the
[`logs`](https://github.com/bevyengine/bevy/blob/main/examples/app/logs.rs)
example and various `RUST_LOG` values.

crates/bevy_log/src/lib.rs

@@ -278,6 +278,7 @@ pub const DEFAULT_FILTER: &str = concat!(
     "symphonia_format_riff::demuxer=warn,",
     "symphonia_format_wav::demuxer=warn,",
     "calloop::loop_logic=error,",
+    "calloop::sources=debug,",
 );
 
 impl Default for LogPlugin {