[libfuzzer] Prevent MSan false positive when printing log with -jobs (#91679)

libfuzzer's -jobs option will, depending on the number of CPUs, spin up
a
WorkerThread and end up printing the log file using CopyFileToErr.
This leads to an MSan false positive. This patch disables the MSan
interceptor checks,
similarly to other instances in https://reviews.llvm.org/D48891

Side-note: this false positive issue first appeared when printf()
was replaced by puts() (90b4d1bc).
The interceptor check was always present; however, MSan does not
check_printf by default.