[release/7.0] Update spa-templates to ref new 7.0 branch (#44134)

- just created release/7.0 in dotnet/spa-templates
  - use it here to enable main in spa-templates to get new branding
- also use latest commit from spa-templates
  - contains a fix for [[C&AI Translation Feedback] - ASP.NET Core incomplete German translation](https://dev.azure.com/ceapex/CEINTL/_workitems/edit/710128)

Author: dougbu

.gitmodules

@@ -9,4 +9,4 @@
 [submodule "src/submodules/spa-templates"]
 	path = src/submodules/spa-templates
 	url = https://github.com/dotnet/spa-templates.git
-	branch = main
+	branch = release/7.0