Sync spec test suite

[github-actions[bot]]

This is an automated pull-request containing the following changes:

Files added

• `tests/spec/transformers/valid/AddMandatoryTags/keep-existing-tags-ampjs/expected_output.html`
• `tests/spec/transformers/valid/AddMandatoryTags/keep-existing-tags-ampjs/input.html`
• `tests/spec/transformers/valid/RewriteAmpUrls/adds_lts_ampjs/expected_output.html`
• `tests/spec/transformers/valid/RewriteAmpUrls/adds_lts_ampjs/input.html`
• `tests/spec/transformers/valid/RewriteAmpUrls/adds_preloads_ampjs/expected_output.html`
• `tests/spec/transformers/valid/RewriteAmpUrls/adds_preloads_ampjs/input.html`