gnu: flint: Disable parallel tests.

* gnu/packages/algebra.scm (flint)[arguments]: Disable parallel tests,
  which makes the build pass on arm.

gnu/packages/algebra.scm

@@ -203,7 +203,8 @@ (define-public flint
     `(("gmp" ,gmp)
       ("mpfr" ,mpfr))) ; header files from both are included by flint/arith.h
    (arguments
-    `(#:phases
+    `(#:parallel-tests? #f ; seems to be necessary on arm
+      #:phases
        (modify-phases %standard-phases
          (replace 'configure
            (lambda* (#:key inputs outputs #:allow-other-keys)