feat: real user as commit author

Previously all commits were authored and committed by

    releaser-pleaser <>

This looked weird when looking at the commit. We now check with the
Forge API for details on the currently authenticated user, and use that
name and email as the commit author. The commit committer stays the same
for now.

In GitHub, the default `$GITHUB_TOKEN` does not allow access to the
required endpoint, so for github the user `github-actions[bot]
<41898282+github-actions[bot]@users.noreply.github.com>` is hardcoded
when the request fails.

internal/git/git.go

@@ -45,6 +45,27 @@ type Releases struct {
 	Stable *Tag
 }
 
+type Author struct {
+	Name  string
+	Email string
+}
+
+func (a Author) signature(when time.Time) *object.Signature {
+	return &object.Signature{
+		Name:  a.Name,
+		Email: a.Email,
+		When:  when,
+	}
+}
+
+func (a Author) String() string {
+	return fmt.Sprintf("%s <%s>", a.Name, a.Email)
+}
+
+var (
+	committer = Author{Name: "releaser-pleaser", Email: ""}
+)
+
 func CloneRepo(ctx context.Context, logger *slog.Logger, cloneURL, branch string, auth transport.AuthMethod) (*Repository, error) {
 	dir, err := os.MkdirTemp("", "releaser-pleaser.*")
 	if err != nil {
@@ -150,15 +171,17 @@ func (r *Repository) UpdateFile(_ context.Context, path string, create bool, upd
 	return nil
 }
 
-func (r *Repository) Commit(_ context.Context, message string) (Commit, error) {
+func (r *Repository) Commit(_ context.Context, message string, author Author) (Commit, error) {
 	worktree, err := r.r.Worktree()
 	if err != nil {
 		return Commit{}, err
 	}
 
+	now := time.Now()
+
 	releaseCommitHash, err := worktree.Commit(message, &git.CommitOptions{
-		Author:    signature(),
-		Committer: signature(),
+		Author:    author.signature(now),
+		Committer: committer.signature(now),
 	})
 	if err != nil {
 		return Commit{}, fmt.Errorf("failed to commit changes: %w", err)
@@ -223,11 +246,3 @@ func (r *Repository) ForcePush(ctx context.Context, branch string) error {
 		Auth:       r.auth,
 	})
 }
-
-func signature() *object.Signature {
-	return &object.Signature{
-		Name:  "releaser-pleaser",
-		Email: "",
-		When:  time.Now(),
-	}
-}