gnu: r-rcpparmadillo: Skip one test on 32-bit systems.

One test in this file fails with an inaccurate comparison, but we cannot
disable just that one test, so we skip the whole file.

* gnu/packages/cran.scm (r-rcpparmadillo)[arguments]: Conditionally skip a
test file.

Change-Id: I29d9bd12fd63c87fd6bb232238418679d079138a

gnu/packages/cran.scm

@@ -7262,6 +7262,13 @@ designed by Cynthia Brewer as described at http://colorbrewer2.org")
                 "07wf1rmlm7hp06vcykmxwbzy01ri28zx20vz39j1sk3w1pck5h7r"))))
     (properties `((upstream-name . "RcppArmadillo")))
     (build-system r-build-system)
+    (arguments
+     (if (target-32bit?)
+         (list
+          #:test-directory "inst/tinytest"
+          ;; Accuracy error.
+          #:skipped-tests '("test_rmultinom.R"))
+         '()))
     (propagated-inputs
      (list r-rcpp))
     (native-inputs (list r-rcpp r-tinytest))