feat: Add img_class argument for get_timber_picture_responsive() #145

Job	Run time
PHP 7.4 \| WP 6.1 \| prefer-stable	6m 11s
PHP 7.4 \| WP 6.1 (MS) \| prefer-stable	4m 10s
PHP 7.4 \| WP latest \| prefer-stable	4m 4s
PHP 7.4 \| WP latest (MS) \| prefer-stable	4m 0s
PHP 7.4 \| WP trunk \| prefer-stable	4m 7s
PHP 8.1 \| WP trunk \| prefer-stable	6m 16s
PHP 8.0 \| WP latest \| prefer-stable	6m 27s
PHP 8.1 \| WP latest \| prefer-stable	4m 6s
PHP 7.4 (Imagick) \| WP latest \| prefer-stable	4m 19s
PHP 7.4 (with coverage) \| WP latest \| prefer-stable	4m 19s
	47m 59s

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