selftests/bpf: Update test_tag to use sha256

selftests/bpf: Update test_tag to use sha256

[ Upstream commit b7f7d76d6e354a5acc711da37cb2829ccf40558f ]

commit 603b44162325 ("bpf: Update the bpf_prog_calc_tag to use SHA256")
changed digest of prog_tag to SHA256 but forgot to update tests
correspondingly. Fix it.

Fixes: 603b44162325 ("bpf: Update the bpf_prog_calc_tag to use SHA256")
Signed-off-by: Xing Guo <higuoxing@gmail.com>
Link: https://lore.kernel.org/r/20251121061458.3145167-1-higuoxing@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>