fix(functions): update function when runtime has changed and redeploy

[norbjd]

Hello 👋

Just a small fix 🐛

When a function runtime is updated from Terraform:

1. the runtime field was actually not updated (e.g. when we GET from the API): this is because this case is simply not handled in the existing code
2. the function is not redeployed. When changing runtime, even if deploy is false, I think most users expect their function to be rebuilt with the new runtime (e.g. when bumping from python310 to python313)

If 2. is controversial, maybe we can just replace:

-	shouldDeploy = shouldDeploy || d.HasChange("runtime")
+	shouldDeploy = shouldDeploy || (d.HasChange("runtime") && deploy)

So, runtime is changed, but function is not redeployed unless explicitly told to do so.

Tests

main.tf:

data "archive_file" "source_zip" {
  type        = "zip"
  source_dir  = "${path.module}/function"
  output_path = "${path.module}/files/function.zip"
}

resource "scaleway_function_namespace" "main" {
  name = "test"
}

resource "scaleway_function" "main" {
  namespace_id = scaleway_function_namespace.main.id
  name         = "test"
  runtime      = "python310"
  deploy        = true
  handler      = "handler.handle"
  privacy      = "public"
  zip_file     = data.archive_file.source_zip.output_path
  zip_hash     = filesha256(data.archive_file.source_zip.output_path)
}

functions/handler.py:

import sys

def handle(event, context):
    return {
        "body": {
            "message": sys.version,
        },
        "statusCode": 200,
    }

Run terraform apply ✔️

Then, change in main.tf:

-  runtime      = "python310"
-  deploy        = true
+  runtime      = "python313"

Running terraform apply redeploys the function ✔️ (we can check the version has changed by calling the function endpoint).

Thanks!

[norbjd]

Note: maybe there are some tests to add, I don't know 😢