git-2.55.0-rc1 t4216 broken TAP failures on non-x86 arch

Hi,

Building git-2.55.0-rc1 today, all non-x86 architectures failed with:

    Test Summary Report
    -------------------
    t4216-log-bloom.sh                               (Wstat: 0 Tests: 167 Failed: 0)
      Parse errors: Unknown TAP token: "--- highbit1/expect 2026-06-17 19:44:07.555797743 +0000"
		    Unknown TAP token: "+++ highbit1/actual 2026-06-17 19:44:07.563651478 +0000"
		    Unknown TAP token: "@@ -1 +1 @@"
		    Unknown TAP token: "-52a9"
		    Unknown TAP token: "+c01f"
    Files=1047, Tests=34680, 1072 wallclock secs ( 7.61 usr  1.61 sys + 395.73 cusr 586.23 csys = 991.18 CPU)
    Result: FAIL

The test output is:

    ok 148 - setup check value of version 1 changed-path
    --- highbit1/expect     2026-06-17 19:44:07.555797743 +0000
    +++ highbit1/actual     2026-06-17 19:44:07.563651478 +0000
    @@ -1 +1 @@
    -52a9
    +c01f
    ok 149 # SKIP check value of version 1 changed-path (missing SIGNED_CHAR_BY_DEFAULT)

This looks like it comes from the following chunk of code in the test:

    # expect will not match actual if char is unsigned by default. Write the test
    # in this way, so that a user running this test script can still see if the two
    # files match. (It will appear as an ordinary success if they match, and a skip
    # if not.)
    if test_cmp highbit1/expect highbit1/actual
    then
	    test_set_prereq SIGNED_CHAR_BY_DEFAULT
    fi
    test_expect_success SIGNED_CHAR_BY_DEFAULT 'check value of version 1 changed-path' '
	    # Only the prereq matters for this test.
	    true
    '

It seems like we could (and perhaps should) redirect the output from test_cmp to a file (or /dev/null).

But... are we expecting these tests to not pass the test_cmp on any non-x86 arch in the first place? Or is this exposing something broken in the test setup (test-tool read-graph bloom-filters) or elsewhere?

Looking at some older builds for non-x86 architectures, they are indeed failing to set the SIGNED_CHAR_BY_DEFAULT prereq.