Add GitHub as valid CI for plugin and theme scaffold

[ernilambar]

Fixes #330

• Add github as valid option for --ci argument
• Add GitHub Actions file template
• When scaffolding, test file is copied to .github/workflows/testing.yml

Note:
For theme, in theme-bootstrap.muscatche, there is code for checking PHP version. So test is exited for PHP greater than 8.0. Is this still valid?

if ( PHP_MAJOR_VERSION >= 8 ) {
	echo "The scaffolded tests cannot currently be run on PHP 8.0+. See https://github.com/wp-cli/scaffold-command/issues/285" . PHP_EOL; // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped
	exit( 1 );
}

[danielbachhuber]

For theme, in theme-bootstrap.muscatche, there is code for checking PHP version. So test is exited for PHP greater than 8.0. Is this still valid?

Can you test?

[ernilambar]

@danielbachhuber I created sample theme and removed that conditional checks. All tests have run successfully. ernilambar/sample-theme#3

Sample plugin check: https://github.com/ernilambar/sample-plugin/pull/3

[ernilambar]

@danielbachhuber It looks ok for me to remove following code from theme-bootstrap.mustache.

if ( PHP_MAJOR_VERSION >= 8 ) {
	echo "The scaffolded tests cannot currently be run on PHP 8.0+. See https://github.com/wp-cli/scaffold-command/issues/285" . PHP_EOL; // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped
	exit( 1 );
}

Should it be done in separate PR?

[danielbachhuber]

Separate PR sounds good