The libsecret credential helper does not mark its build artifact as
ignored, so running "make" results in a dirty working tree.
Mark the "git-credential-libsecret" binary as ignored to avoid the above.
Co-authored-by: Jeff King <redacted> Signed-off-by: Jeff King <redacted> Signed-off-by: Taylor Blau <redacted> Signed-off-by: Junio C Hamano <redacted>