updatecli: add condition for assets.json

[v1v]

This should help when the assets.json is not available.

Closes #571

$ GO_MINOR=1.24 GITHUB_TOKEN=$(gh auth token) \
  GITHUB_ACTOR=v1v BRANCH=main \
  updatecli apply --config .github/updatecli.d/bump-golang.yml

condition: condition#is-not-available
--------------------------
✗ condition on file ["https://aka.ms/golang/release/latest/go1.24.2.assets.json"] passed

condition: condition#dockerTag
-------------------
✔ docker image golang:1.24.2 found

condition: condition#is-already-updated
----------------------------
The shell 🐚 command "/bin/sh /var/folders/t7/ghqdh8cx2g12pwb_w0ncmw900000gn/T/updatecli/bin/930c7a665b94254478ed7050ad905da920eb37a219b5e35b90beba13d0afcab2.sh" ran successfully with the following output:
----
----
✔ shell condition of type "console/output", passing

target: target#update-go-makefile.common
--------------------------------

target: target#update-go-versions
-------------------------

target: target#update-go-version
------------------------

ACTIONS
========

Bump golang-version to latest version
  => [Automation] Bump Golang version to 1.24.2

Existing GitHub pull request found: https://github.com/elastic/golang-crossbuild/pull/570
Existing GitHub pull request found: https://github.com/elastic/golang-crossbuild/pull/570

=============================

SUMMARY:

- Bump golang-version to latest version:
	Source:
		✔ [latestGoVersion] Get Latest Go Release
		✔ [minor] Get minor version
	Condition:
		✔ [dockerTag] Is docker image golang:1.24.2 published
		✔ [is-already-updated] Is version '1.24.2' not updated in 'go/Makefile.common'?
		✗ [is-not-available] Is assets.json available?
	Target:
		- [update-go-makefile.common] 
		- [update-go-version] 
		- [update-go-versions] 


Run Summary
===========
Pipeline(s) run:
  * Changed:	0
  * Failed:	0
  * Skipped:	1
  * Succeeded:	0
  * Total:	1

[mergify]

This pull request does not have a backport label. Could you fix it @v1v? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v./d./d is the label to automatically backport to the 1./d branch. /d is the digit
  NOTE: backport-skip has been added to this pull request.

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: 4116c85

cc @v1v

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: 4116c85

cc @v1v

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: 4116c85

cc @v1v