Issue #3400334 by mstrelan, quietone, smustgrave: Add declare(strict_types=1) to all test modules

...nounce_feed_test/src/AnnounceTestHttpClientMiddleware.php

...ounce_feed_test/src/Controller/AnnounceTestController.php

...s/modules/basic_auth_test/src/BasicAuthTestController.php

...ests/modules/big_pipe_bypass_js/big_pipe_bypass_js.module

.../big_pipe_regression_test/big_pipe_regression_test.module

...e_regression_test/src/BigPipeRegressionTestController.php

...big_pipe/tests/modules/big_pipe_test/big_pipe_test.module

...modules/big_pipe_test/src/BigPipePlaceholderTestCases.php

...tests/modules/big_pipe_test/src/BigPipeTestController.php

...g_pipe_test/src/EventSubscriber/BigPipeTestSubscriber.php

.../tests/modules/big_pipe_test/src/Form/BigPipeTestForm.php

.../modules/block/tests/modules/block_test/block_test.module

.../tests/modules/block_test/src/BlockRenderAlterContent.php

.../block_test/src/ContextProvider/MultipleStaticContext.php

.../block_test/src/Controller/TestMultipleFormController.php

...ts/modules/block_test/src/Form/FavoriteAnimalTestForm.php

...ules/block/tests/modules/block_test/src/Form/TestForm.php

...s/modules/block_test/src/Plugin/Block/TestAccessBlock.php

...es/block_test/src/Plugin/Block/TestBlockInstantiation.php

...ts/modules/block_test/src/Plugin/Block/TestCacheBlock.php