fix: add .tar.gz extension to source archive name template

- Terraform Registry expects the source file to be named with .tar.gz extension
- Update name_template to include the extension in the filename
- Fixes 'missing files in request body' error when publishing to registry

Author: Trozz

.goreleaser.yml

@@ -152,5 +152,5 @@ snapshot:
 # Source configuration
 source:
   enabled: true
-  name_template: "{{ .ProjectName }}_{{ .Version }}_source"
+  name_template: "{{ .ProjectName }}_{{ .Version }}_source.tar.gz"
   format: "tar.gz"