Move build constraints above the license header

gofmt -s wants the //go:build line first in the file, and the rest of
the repo follows that layout (see internal/fileutil/fileutil_unix.go).
Without this the golangci-lint job fails on the formatter check.

Signed-off-by: Mukul <nmukul32@gmail.com>

internal/plugin/installer/umask_unix_test.go

@@ -1,3 +1,5 @@
+//go:build !windows
+
 /*
 Copyright The Helm Authors.
 Licensed under the Apache License, Version 2.0 (the "License");
@@ -13,8 +15,6 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-//go:build !windows
-
 package installer
 
 import "syscall"

internal/plugin/installer/umask_windows_test.go

@@ -1,3 +1,5 @@
+//go:build windows
+
 /*
 Copyright The Helm Authors.
 Licensed under the Apache License, Version 2.0 (the "License");
@@ -13,8 +15,6 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-//go:build windows
-
 package installer
 
 // posixPermsSupported reports whether the platform honors POSIX file