Remove need for write permissions during scaffolding

[flotwig]

Current behavior:

Cypress's scaffolding will prevent tests from proceeding if it fails.

Desired behavior:

When Cypress's scaffolding fails, warn, set the config value that failed to false (ex. supportFile: false, pluginsFile: false and continue on.

This is especially important in run mode, where pluginsFile is the only file scaffolded, and failures to scaffold lead to test failure:

cypress/packages/server/lib/project.js

Lines 96 to 104 in 6960f7c

	// TODO: we currently always scaffold the plugins file
	// even when headlessly or else it will cause an error when
	// we try to load it and it's not there. We must do this here
	// else initialing the plugins will instantly fail.
	if (cfg.pluginsFile) {
	debug('scaffolding with plugins file %s', cfg.pluginsFile)
	return scaffold.plugins(path.dirname(cfg.pluginsFile), cfg)
	}

Related: #7126

[flotwig]

Fixed, see related issues.