upload-artifact@v7 direct uploads do not round-trip with download-artifact@v8

Bug report info

act version: 0.2.89

Command used with act

act push --artifact-server-path ./artifacts

Describe issue

• actions/upload-artifact@v7 supports uploading one file directly with archive: false.
• This is separate from the basic v7/v8 request compatibility tracked in #6114. Accepting the new mime_type field is not enough because act currently discards its value.
• actions/download-artifact@v8 uses the blob response Content-Type to decide whether to extract it and Content-Disposition to recover the filename.
• Without that metadata, the direct download uses the fallback filename artifact instead of the uploaded filename.
• Direct artifacts should retain their MIME type and download with their original filename.

Workflow content

on:
  push:
jobs:
  artifacts:
    runs-on: ubuntu-latest
    steps:
      - run: echo Direct artifact > direct.txt

      - uses: actions/upload-artifact@v7
        with:
          path: direct.txt
          archive: false

      - uses: actions/download-artifact@v8
        with:
          name: direct.txt
          path: out

      - run: cmp direct.txt out/direct.txt

Relevant log output

Downloading raw file (non-zip) to: .../out/artifact
cmp: out/direct.txt: No such file or directory

Additional information

• With archive: false, upload-artifact uses the source basename as the artifact name.
• The artifact server needs to preserve the request MIME type and return appropriate Content-Type and Content-Disposition headers for the download.