test: generate a minimal RPM in pure Go instead of a committed fixture

Removes the committed .rpm binary (gitignored, so it broke clean checkouts)
and the rpmbuild dependency. testsupport.MinimalRPM builds a valid-enough
RPM header in-memory for cavaliergopher/rpm to parse, used by both the rpm
provider test and the full-stack server repodata test.

internal/provider/rpm/rpm_meta_test.go

@@ -7,16 +7,14 @@ import (
 	"io"
 	"net/http"
 	"net/http/httptest"
-	"os"
 	"strings"
 	"testing"
 
 	"git.unkin.net/unkin/artifactapi/internal/provider"
+	"git.unkin.net/unkin/artifactapi/internal/testsupport"
 	"git.unkin.net/unkin/artifactapi/pkg/models"
 )
 
-const fixtureRPM = "testdata/e2e-testpkg-1.0-1.noarch.rpm"
-
 type fakeBlobReader struct{ data []byte }
 
 func (f fakeBlobReader) Download(_ context.Context, _ string) (io.ReadCloser, int64, error) {
@@ -82,10 +80,7 @@ func TestRPMValidateUpload(t *testing.T) {
 }
 
 func TestRPMAfterUpload(t *testing.T) {
-	data, err := os.ReadFile(fixtureRPM)
-	if err != nil {
-		t.Fatalf("fixture: %v", err)
-	}
+	data := testsupport.MinimalRPM("e2e-testpkg", "1.0", "1", "noarch")
 	store := &fakeMetaStore{}
 	(&Provider{}).AfterUpload(context.Background(), "myrepo", "Packages/e2e-testpkg-1.0-1.noarch.rpm",
 		"sha256:deadbeef", fakeBlobReader{data: data}, store)