bump go to 1.21 (#546)

* bump go to 1.21

Signed-off-by: yxxhero <[email protected]>

Author: yxxhero

.github/workflows/lint.yaml

@@ -21,4 +21,4 @@ jobs:
           go-version-file: 'go.mod'
       - uses: golangci/golangci-lint-action@v3
         with:
-          version: v1.55.1
+          version: v1.55.2

go.mod

@@ -1,6 +1,6 @@
 module github.com/databus23/helm-diff/v3
 
-go 1.20
+go 1.21
 
 require (
 	github.com/Masterminds/semver v1.5.0