Fix null source bug with null source for pages project

[Cyb3r-Jak3]

Fixes #1897

I forget to set the project source, which caused it to not be created. Unit tests didn't seem to catch it 😬

[github-actions]

changelog detected ✅

[jacobbednarz]

acceptance tests are good, thanks!

TF_ACC=1 go test $(go list ./...) -v -run "^TestAccCloudflarePagesProject_" -count 1 -parallel 1 -timeout 120m -parallel 1
?       github.com/cloudflare/terraform-provider-cloudflare     [no test files]
=== RUN   TestAccCloudflarePagesProject_BuildConfig
--- PASS: TestAccCloudflarePagesProject_BuildConfig (10.34s)
=== RUN   TestAccCloudflarePagesProject_DeploymentConfig
--- PASS: TestAccCloudflarePagesProject_DeploymentConfig (9.99s)
=== RUN   TestAccCloudflarePagesProject_DirectUpload
--- PASS: TestAccCloudflarePagesProject_DirectUpload (10.23s)
=== RUN   TestAccCloudflarePagesProject_PreviewOnly
--- PASS: TestAccCloudflarePagesProject_PreviewOnly (10.52s)
=== RUN   TestAccCloudflarePagesProject_ProductionOnly
--- PASS: TestAccCloudflarePagesProject_ProductionOnly (9.69s)
PASS
PASS    github.com/cloudflare/terraform-provider-cloudflare/internal/provider   54.986s
?       github.com/cloudflare/terraform-provider-cloudflare/tools/cmd/changelog-check   [no test files]
?       github.com/cloudflare/terraform-provider-cloudflare/tools/cmd/maintainer-only-file-check        [no test files]
?       github.com/cloudflare/terraform-provider-cloudflare/tools/cmd/tf-log-check      [no test files]
?       github.com/cloudflare/terraform-provider-cloudflare/version     [no test files]
PASS

[github-actions]

This functionality has been released in v3.24.0 of the Terraform Cloudflare Provider.

Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

For further feature requests or bug reports with this functionality, please create a new GitHub issue following the template. Thank you!