fix: use showFileAtRefBase64 to read per-commit file contents (#3744)

* GitCommandManager: add a function to get a file's contents at a specific revision

* use showFileAtRef instead of readFileBase64

* Teach GitCommandManager.exec about an object of exec parameters so we can add more

* Encode the showFiletRef output as base64 out of the gate

* Fix missing async for function

* Use Buffer.concat to avoid issues with partial data streams

* formatting

---------

Co-authored-by: gustavderdrache <alex.ford@determinate.systems>

src/create-pull-request.ts

@@ -211,6 +211,7 @@ export async function createPullRequest(inputs: Inputs): Promise<void> {
         const stashed = await git.stashPush(['--include-untracked'])
         await git.checkout(inputs.branch)
         const pushSignedCommitsResult = await ghBranch.pushSignedCommits(
+          git,
           result.branchCommits,
           result.baseCommit,
           repoPath,