MDL-81522 phpunit: Add missing void return type to all tests

While this change is not 100% required now, it's good habit
and we are checking for it since Moodle 4.4.

All the changes in this commit have been applied automatically
using the moodle.PHPUnit.TestReturnType sniff and are, exclusively
adding the ": void" return types when missing.

lib/phpunit/tests/basic_test.php

@@ -42,7 +42,7 @@ class basic_test extends \basic_testcase {
      * Tests that bootstrapping has occurred correctly
      * @return void
      */
-    public function test_bootstrap() {
+    public function test_bootstrap(): void {
         global $CFG;
 
         // The httpswwwroot has been deprecated, we keep it as an alias for backwards compatibility with plugins only.
@@ -55,7 +55,7 @@ class basic_test extends \basic_testcase {
      * This is just a verification if I understand the PHPUnit assert docs right --skodak
      * @return void
      */
-    public function test_assert_behaviour() {
+    public function test_assert_behaviour(): void {
         // Arrays.
         $a = array('a', 'b', 'c');
         $b = array('a', 'c', 'b');
@@ -120,7 +120,7 @@ class basic_test extends \basic_testcase {
      * Make sure there are no sloppy Windows line endings
      * that would break our tests.
      */
-    public function test_lineendings() {
+    public function test_lineendings(): void {
         $string = <<<STRING
 a
 b
@@ -132,7 +132,7 @@ STRING;
     /**
      * Make sure asserts in setUp() do not create problems.
      */
-    public function test_setup_assert() {
+    public function test_setup_assert(): void {
         $this->assertTrue($this->testassertexecuted);
         $this->testassertexecuted = false;
     }
@@ -140,7 +140,7 @@ STRING;
     /**
      * Test assert Tag
      */
-    public function test_assert_tag() {
+    public function test_assert_tag(): void {
         // This should succeed.
         self::assertTag(['id' => 'testid'], "<div><span id='testid'></span></div>");
         $this->expectException(\PHPUnit\Framework\ExpectationFailedException::class);