gnu: lz4: Run tests sequentially.

* gnu/packages/compression.scm (lz4)[arguments]: Add #:parallel-tests?.

gnu/packages/compression.scm

@@ -804,6 +804,7 @@ decompression of some loosely related file formats used by Microsoft.")
        ("valgrind" ,valgrind)))
     (arguments
      `(#:test-target "test"
+       #:parallel-tests? #f      ;occasional failures when running in parallel
        #:make-flags (list (string-append "CC=" ,(cc-for-target))
                           (string-append "prefix=" (assoc-ref %outputs "out")))
        #:phases