🐛 enable import-shadowing linter in .golangci.yml files

This PR adds the `import-shadowing` linter to all `.golangci.yml` configuration files across test projects and templates.
The `import-shadowing` linter detects cases where a package import shadows an existing variable, which can lead to subtle bugs.

Author: kersten

docs/book/src/cronjob-tutorial/testdata/project/.golangci.yml

@@ -45,3 +45,4 @@ linters-settings:
   revive:
     rules:
       - name: comment-spacings
+      - name: import-shadowing

docs/book/src/getting-started/testdata/project/.golangci.yml

@@ -45,3 +45,4 @@ linters-settings:
   revive:
     rules:
       - name: comment-spacings
+      - name: import-shadowing

docs/book/src/multiversion-tutorial/testdata/project/.golangci.yml

@@ -45,3 +45,4 @@ linters-settings:
   revive:
     rules:
       - name: comment-spacings
+      - name: import-shadowing

pkg/plugins/golang/v4/scaffolds/internal/templates/golangci.go

@@ -88,4 +88,5 @@ linters-settings:
   revive:
     rules:
       - name: comment-spacings
+      - name: import-shadowing
 `

testdata/project-v4-multigroup/.golangci.yml

@@ -45,3 +45,4 @@ linters-settings:
   revive:
     rules:
       - name: comment-spacings
+      - name: import-shadowing

testdata/project-v4-with-plugins/.golangci.yml

@@ -45,3 +45,4 @@ linters-settings:
   revive:
     rules:
       - name: comment-spacings
+      - name: import-shadowing

testdata/project-v4/.golangci.yml

@@ -45,3 +45,4 @@ linters-settings:
   revive:
     rules:
       - name: comment-spacings
+      - name: import-shadowing