BUG: Pinned-Dependencies fails to handle Dockerfiles with here-docs

[pnacht]

Describe the bug
Dockerfiles with here-docs crash the Pinned-Deps check

Reproduction steps
Run scorecard --checks Pinned-Dependencies --repo moby/moby (also works with --repo distribution/distribution)

Error: check runtime error: Pinned-Dependencies: internal error: error parsing shell code: Dockerfile:1:1: unclosed here-document 'EOT'
2023/07/31 16:52:39 error during command execution: check runtime error: Pinned-Dependencies: internal error: error parsing shell code: Dockerfile:1:1: unclosed here-document 'EOT'

moby/moby/Dockerfile and distribution/distribution/dockerfiles/vendor.Dockerfile have RUN commands such as

RUN --mount=target=/context \
    --mount=target=.,type=tmpfs  \
    --mount=target=/go/pkg/mod,type=cache <<EOT
  set -e
  rsync -a /context/. .
  go mod tidy
  go mod vendor
  mkdir /out
  cp -r go.mod go.sum vendor /out
EOT

Expected behavior
The Dockerfile should be correctly parsed.

[jkreileder]

#3774 fixes the problem for moby/moby:

$ go run main.go --checks Pinned-Dependencies --repo moby/moby
Starting [Pinned-Dependencies]
Finished [Pinned-Dependencies]

RESULTS
-------
Aggregate score: 0.0 / 10

Check scores:
|--------|---------------------|--------------------------------|--------------------------------------------------------------------------------|
| SCORE  |        NAME         |             REASON             |                           DOCUMENTATION/REMEDIATION                            |
|--------|---------------------|--------------------------------|--------------------------------------------------------------------------------|
| 0 / 10 | Pinned-Dependencies | dependency not pinned by hash  | https://github.com/ossf/scorecard/blob/main/docs/checks.md#pinned-dependencies |
|        |                     | detected -- score normalized   |                                                                                |
|        |                     | to 0                           |                                                                                |
|--------|---------------------|--------------------------------|--------------------------------------------------------------------------------|

And it also fixes the problem for me:

$ scorecard --checks Pinned-Dependencies --repo=jkreileder/cf-ips-to-hcloud-fw
[...]
Error: check runtime error: Pinned-Dependencies: internal error: error parsing shell code: Dockerfile:1:1: unclosed here-document 'EOF'
2024/01/06 17:55:47 error during command execution: check runtime error: Pinned-Dependencies: internal error: error parsing shell code: Dockerfile:1:1: unclosed here-document 'EOF'
$ go run main.go --checks Pinned-Dependencies --repo=jkreileder/cf-ips-to-hcloud-fw
Starting [Pinned-Dependencies]
Finished [Pinned-Dependencies]

RESULTS
-------
Aggregate score: 10.0 / 10

Check scores:
|---------|---------------------|-----------------------------|--------------------------------------------------------------------------------|
|  SCORE  |        NAME         |           REASON            |                           DOCUMENTATION/REMEDIATION                            |
|---------|---------------------|-----------------------------|--------------------------------------------------------------------------------|
| 10 / 10 | Pinned-Dependencies | all dependencies are pinned | https://github.com/ossf/scorecard/blob/main/docs/checks.md#pinned-dependencies |
|---------|---------------------|-----------------------------|--------------------------------------------------------------------------------|