Add a comment to 90-test_external.t to explain why we need filter_run

plan tests => 1;

indir $ENV{BORING_RUNNER_DIR} => sub {

    ok(filter_run(executable(["go", "test", "-shim-path",

    ok(filter_run(cmd(["go", "test", "-shim-path",

                      srctop_file("test", "ossl_shim", "ossl_shim"),

                      "-shim-config",

                              srctop_file("test", "ossl_shim",

                                          "ossl_config.json"),

                      srctop_file("test", "ossl_shim", "ossl_config.json"),

                      "-pipe"])),

        "running external tests");

}, create => 0, cleanup => 0;

# Filter the output so that the "ok" printed by go test doesn't confuse

# Test::More. Without that it thinks there has been one more test run than was

# planned

sub filter_run {

    my $cmd = cmdstr(shift);

    open(PIPE, "-|", $cmd);