distro: sed: Patch references to /bin/sh in the test suite.

* distro/packages/base.scm (sed): Add `patch-test-suite' phase.

distro/packages/base.scm

@@ -97,6 +97,17 @@ lines.")
               "13wlsb4sf5d5a82xjhxqmdvrrn36rmw5f0pl9qyb9zkvldnb7hra"))))
    (build-system gnu-build-system)
    (synopsis "GNU sed, a batch stream editor")
+   (arguments
+    `(#:phases (alist-cons-before
+                'patch-source-shebangs 'patch-test-suite
+                (lambda* (#:key inputs #:allow-other-keys)
+                  (let ((bash (assoc-ref inputs "bash")))
+                    (patch-makefile-SHELL "testsuite/Makefile.tests")
+                    (substitute* '("testsuite/bsd.sh"
+                                   "testsuite/bug-regex9.c")
+                      (("/bin/sh")
+                       (string-append bash "/bin/bash")))))
+                %standard-phases)))
    (description
     "Sed (stream editor) isn't really a true text editor or text processor.
 Instead, it is used to filter text, i.e., it takes text input and performs