fix: skip only absolute filesystem dirs

[nikpivkin]

Description

Related issues

• Close fix: skip only absolute filesystem dirs #6651

Checklist

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• I've followed the conventions in the PR title.
• I've added tests that prove my fix is effective or that my feature works.
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[knqyf263]

@DmitriyLewen Can you please test this change?

[DmitriyLewen]

@nikpivkin
These changes break image scanning:

➜ cat Dockerfile 
FROM ubuntu

COPY log4j-core-2.16.0.jar /sys/log4j-core-2.16.0.jar

COPY log4j-core-2.16.0.jar /dev/log4j-core-2.16.0.jar

➜ ./trivy image 6657 -f json --list-all-pkgs | jq '.Results[].Packages[] | select(.Name=="org.apache.logging.log4j:log4j-core")'
{
  "Name": "org.apache.logging.log4j:log4j-core",
  "Identifier": {
    "PURL": "pkg:maven/org.apache.logging.log4j/[email protected]",
    "UID": "1b4b8d0c2ceb5ca0"
  },
  "Version": "2.16.0",
  "Layer": {
    "DiffID": "sha256:74750d50e4fa74a48fe7866ed1e7f5f6f16c03e9504bf11412d12b7768e5e00d"
  },
  "FilePath": "sys/log4j-core-2.16.0.jar"
}
{
  "Name": "org.apache.logging.log4j:log4j-core",
  "Identifier": {
    "PURL": "pkg:maven/org.apache.logging.log4j/[email protected]",
    "UID": "a983edae42e3121e"
  },
  "Version": "2.16.0",
  "Layer": {
    "DiffID": "sha256:d8b26baefb6f0e55808ab1a5cb920497cabeac307b1cf46d06d5b27b68fc5924"
  },
  "FilePath": "dev/log4j-core-2.16.0.jar"
}

rootfs and fs modes also don't work (/proc dir is scanned):

root@ce1618593f59:/# ./trivy fs / -f json --list-all-pkgs
...
2024-05-14T06:36:48Z	FATAL	Fatal error	filesystem scan error: scan error: scan failed: failed analysis: walk filesystem: walk dir error: unknown error with /proc/3098/fdinfo/11: file info error: lstat /proc/3098/fdinfo/11: no such file or directory
root@ce1618593f59:/# ./trivy rootfs / -f json --list-all-pkgs
...
2024-05-14T06:36:51Z	FATAL	Fatal error	rootfs scan error: scan error: scan failed: failed analysis: walk filesystem: walk dir error: unknown error with /proc/3111/fdinfo/11: file info error: lstat /proc/3111/fdinfo/11: no such file or directory