appender: add fallback to file creation date

When using the linux-musl target for rust, the file creation time
cannot be retrieved, as the current version does not support it yet (
This will be fixed with [0]). In the meantime, we parse the datetime
from the filename and use that as a fallback.

Fixes: tokio-rs#2999

[0]: rust-lang/rust#125692

Author: kaffarell

tracing-appender/src/rolling.rs

@@ -602,7 +602,10 @@ impl Inner {
                     return None;
                 }
 
-                let created = metadata.created().ok()?;
+                let created = metadata.created().ok().or_else(|| {
+                    let datetime = OffsetDateTime::parse(filename, &self.date_format).ok()?;
+                    Some(datetime.into())
+                })?;
                 Some((entry, created))
             })
             .collect::<Vec<_>>()