runtime: Make SetupOCIConfigFile clean up after itself

SetupOCIConfigFile creates a temporary directory with os.MkDirTemp().  This
means the callers need to register a deferred function to remove it again.
At least one of them was commented out meaning that a /temp/katatest-
directory was leftover after the unit tests ran.

Change to using t.TempDir() which as well as better matching other parts of
the tests means the testing framework will handle cleaning it up.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

src/runtime/pkg/katatestutils/utils.go

@@ -346,11 +346,10 @@ func IsInGitHubActions() bool {
 func SetupOCIConfigFile(t *testing.T) (rootPath string, bundlePath, ociConfigFile string) {
 	assert := assert.New(t)
 
-	tmpdir, err := os.MkdirTemp("", "katatest-")
-	assert.NoError(err)
+	tmpdir := t.TempDir()
 
 	bundlePath = filepath.Join(tmpdir, "bundle")
-	err = os.MkdirAll(bundlePath, testDirMode)
+	err := os.MkdirAll(bundlePath, testDirMode)
 	assert.NoError(err)
 
 	ociConfigFile = filepath.Join(bundlePath, "config.json")