Fix watch path to avoid node_modules

[colinrotherham]

Description

This PR prevents gulp watch responding to node_modules changes

It was caused by npm workspace support in #1261 which makes node_modules/nhsuk-frontend a symlink

Console output

Example console output when **/*.njk changes matched both:

'packages/components/**/*.njk' # source path
'node_modules/nhsuk-frontend/packages/components/**/*.njk' # symlink path

[Browsersync] Serving files from: dist/app
[09:42:48] Finished 'serve' after 123 ms
[09:42:48] Finished 'docs:serve' after 124 ms
[09:42:48] Finished 'default' after 126 ms
[09:43:15] Starting 'buildHTML'...
[09:43:15] Finished 'buildHTML' after 364 ms
[09:43:16] Starting 'buildHTML'...
[09:43:16] Finished 'buildHTML' after 246 ms
[09:43:16] Starting 'buildHTML'...
[09:43:16] Finished 'buildHTML' after 158 ms
[09:43:17] Starting 'buildHTML'...
[09:43:17] Finished 'buildHTML' after 173 ms
[09:43:17] Starting 'buildHTML'...
[09:43:17] Finished 'buildHTML' after 169 ms
[09:43:17] Starting 'buildHTML'...
[09:43:18] Finished 'buildHTML' after 167 ms
[09:43:18] Starting 'buildHTML'...
[09:43:18] Finished 'buildHTML' after 153 ms
[09:43:18] Starting 'buildHTML'...
[09:43:18] Finished 'buildHTML' after 155 ms
[09:43:19] Starting 'buildHTML'...
[09:43:19] Finished 'buildHTML' after 156 ms
[09:43:19] Starting 'buildHTML'...
[09:43:19] Finished 'buildHTML' after 149 ms
[09:43:20] Starting 'buildHTML'...
[09:43:20] Finished 'buildHTML' after 179 ms

Checklist

• Tested against our testing policy (Resolution, Browser & Accessibility)
• Follows our coding standards and style guide
• CHANGELOG entry

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud