Fix form submission test and one more missing theme in tests

tests/src/Functional/PhpFilterTest.php

@@ -35,7 +35,7 @@ class PhpFilterTest extends PhpTestBase {
     $edit = [];
     $edit['body[0][format]'] = $this->phpCodeFormat->id();
     $this->drupalGet('node/' . $node->id() . '/edit');
-    $this->submitForm($edit, t('Save'));
+    $this->submitForm($edit, 'Save');
     $this->assertSession()->responseContains(t('@type %title has been updated.', ['@type' => 'Basic page', '%title' => $node->toLink($node->getTitle())->toString()]));
 
     // Make sure that the PHP code shows up as text.

tests/src/Functional/PhpUninstallTest.php

@@ -11,6 +11,8 @@ use Drupal\Tests\BrowserTestBase;
  */
 class PhpUninstallTest extends BrowserTestBase {
 
+  protected $defaultTheme = 'stark';
+
   /**
    * Modules to enable.
    *
@@ -47,9 +49,9 @@ class PhpUninstallTest extends BrowserTestBase {
     $edit = [];
     $edit['uninstall[php]'] = TRUE;
     $this->drupalGet('admin/modules/uninstall');
-    $this->submitForm($edit, t('Uninstall'));
+    $this->submitForm($edit, 'Uninstall');
     $this->assertSession()->pageTextContains(t('Would you like to continue with uninstalling the above?'));
-    $this->submitForm([], t('Uninstall'));
+    $this->submitForm([], 'Uninstall');
     $this->assertSession()->pageTextContains(t('The selected modules have been uninstalled.'));
   }