gnu: docker: Replace tini by tini-static.

The dynamically linked tini could fail in some environments, causing 'docker
run' to exit with the following unhelpful error message:

  standard_init_linux.go:219: exec user process caused: no such file or
  directory

Use the statically linked tini binary instead, which should work everywhere.

* gnu/packages/docker.scm (docker)[phases]{patch-paths}: Replace 'tini' by
'tini-static'.

gnu/packages/docker.scm

@@ -382,12 +382,12 @@ built-in registry server of Docker.")
                (("DefaultInitBinary = .*")
                 (string-append "DefaultInitBinary = \""
                                (assoc-ref inputs "tini")
-                               "/bin/tini\"\n")))
+                               "/bin/tini-static\"\n")))
              (substitute* "daemon/config/config_common_unix_test.go"
                (("expectedInitPath: \"docker-init\"")
                 (string-append "expectedInitPath: \""
                                (assoc-ref inputs "tini")
-                               "/bin/tini\"")))
+                               "/bin/tini-static\"")))
              (substitute* "vendor/github.com/moby/buildkit/executor/runcexecutor/executor.go"
                (("var defaultCommandCandidates = .*")
                 (string-append "var defaultCommandCandidates = []string{\""