Fix redis-check-aof incorrectly considering data in manifest format a…

…s MP-AOF (#12958)

The check in fileIsManifest misjudged the manifest file. For example,
if resp aof contains "file", it will be considered a manifest file and
the check will fail:
```
*3
$3
set
$4
file
$4
file
```

In #12951, if the preamble aof also contains it, it will also fail.
Fixes #12951.

the bug was happening if the the word "file" is mentioned
in the first 1024 lines of the AOF. and now as soon as it finds
a non-comment line it'll break (if it contains "file" or doesn't)

(cherry picked from commit da727ad)

tests/integration/aof.tcl

@@ -495,7 +495,7 @@ tags {"aof external:skip"} {
 
     test {Test valkey-check-aof for old style rdb-preamble AOF} {
         catch {
-            exec src/valkey-check-aof tests/assets/rdb-preamble.aof
+	    exec src/valkey-check-aof tests/assets/rdb-preamble.aof
         } result
         assert_match "*Start checking Old-Style AOF*RDB preamble is OK, proceeding with AOF tail*is valid*" $result
     }