dm-integrity: replace forgeable discard filler with a keyed sector marker

{
                    "product": "Linux",
                    "vendor": "Linux",
                    "defaultStatus": "unaffected",
                    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                    "programFiles": [
                        "Documentation/admin-guide/device-mapper/dm-ima.rst",
                        "Documentation/admin-guide/device-mapper/dm-integrity.rst",
                        "drivers/md/dm-integrity.c"
                    ],
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                    ]
                }

{
                    "product": "Linux",
                    "vendor": "Linux",
                    "defaultStatus": "affected",
                    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                    "programFiles": [
                        "Documentation/admin-guide/device-mapper/dm-ima.rst",
                        "Documentation/admin-guide/device-mapper/dm-integrity.rst",
                        "drivers/md/dm-integrity.c"
                    ],
                    "versions": [
                        {
                            "version": "5.7",
                            "status": "affected"
                        },
                        {
                            "version": "0",
                            "lessThan": "5.7",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "6.12.114",
                            "lessThanOrEqual": "6.12.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "6.18.52",
                            "lessThanOrEqual": "6.18.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "7.2.6",
                            "lessThanOrEqual": "7.2.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "7.3",
                            "lessThanOrEqual": "*",
                            "status": "unaffected",
                            "versionType": "original_commit_for_fix"
                        }
                    ]
                }