ci: update gvm to v0.6.0 to fix Go download failures

The CI builds were failing with HTTP 403 errors when downloading Go:

  gvm: error: failed downloading from https://storage.googleapis.com/golang/go1.24.7.windows-amd64.zip: download failed with http status 403

See andrewkroh/gvm#117 that describes the issue
on gvm's side.

Tested locally:
  $ /tmp/gvm-0.6.0 --version
  0.6.0
  $ eval "$(/tmp/gvm-0.6.0 1.24.7)" && go version
  go version go1.24.7 linux/amd64

Updated gvm version in:
- .buildkite/pipeline.yml (SETUP_GVM_VERSION env var)
- .buildkite/scripts/run-win-tests.ps1 (hardcoded URL)

This aligns with the beats repository configuration.

Author: orestisfl

.buildkite/pipeline.yml

@@ -1,7 +1,7 @@
 # yaml-language-server: $schema=https://raw.githubusercontent.com/buildkite/pipeline-schema/main/schema.json
 
 env:
-  SETUP_GVM_VERSION: 'v0.5.2'
+  SETUP_GVM_VERSION: 'v0.6.0'
   LINUX_AGENT_IMAGE: "golang:${GO_VERSION}"
   WINDOWS_AGENT_IMAGE: "family/core-windows-2022"
 

.buildkite/scripts/run-win-tests.ps1

@@ -13,7 +13,7 @@ function fixCRLF {
 function withGolang($version) {
     Write-Host "-- Install golang --"
     [Net.ServicePointManager]::SecurityProtocol = "tls12"
-    Invoke-WebRequest -URI https://github.com/andrewkroh/gvm/releases/download/v0.5.2/gvm-windows-amd64.exe -Outfile C:\Windows\System32\gvm.exe
+    Invoke-WebRequest -URI https://github.com/andrewkroh/gvm/releases/download/v0.6.0/gvm-windows-amd64.exe -Outfile C:\Windows\System32\gvm.exe
     gvm --format=powershell $version | Invoke-Expression
     go version
     go env -w GOBIN="$(go env GOROOT)\bin"