sbsign: write unaligned signature size into WIN_CERTIFICATE header

The inclusion of padding bytes in the signature size can lead to the signature
being rejected by strict PKCS7 parsers. Meanwhile, according to [1], the parser
of the WIN_CERTIFICATE structure is expected to round up the value of dwLength
to an 8-byte multiple. This also matches the behaviour of the sbsign tool from
sbsigntools.

Fixes #42884

[1] https://learn.microsoft.com/en-us/windows/win32/debug/pe-format#the-attribute-certificate-table-image-only

Signed-off-by: Vsevolod Kozlov <zaba@mm.st>
(cherry picked from commit 93aadbf968)

src/sbsign/sbsign.c

@@ -659,7 +659,7 @@ static int verb_sign(int argc, char *argv[], uintptr_t _data, void *userdata) {
                    &(WIN_CERTIFICATE_HEADER) {
                            .wRevision = htole16(0x200),
                            .wCertificateType = htole16(0x0002), /* PKCS7 signedData */
-                           .dwLength = htole32(ROUND_UP(certsz, 8)),
+                           .dwLength = htole32(certsz),
                    },
                    sizeof(WIN_CERTIFICATE_HEADER),
                    end);