Skip test while snapshot downloader cannot handle downgrades

[AndersonQ]

Commit title: skip test while snapshot downloader cannot handle downgrades
Commit message: The snapshot downloader cannot handle downgrades what brakes this test between releases. An issue to fix the snapshot dowloader is filed: #3313

What does this PR do?

Rename TestStandaloneUpgradeWithGPGFallback to TestStandaloneDowngradeWithGPGFallback and skip it

Why is it important?

The snapshot downloader cannot handle downgrades what brakes this test between releases.

Checklist

• My code follows the style guidelines of this project
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [ ] I have made corresponding change to the default configuration files
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] I have added an entry in ./changelog/fragments using the changelog tool
• [ ] I have added an integration test or an E2E test

Related issues

• Relates Snapshot downloader cannot downgrade  #3313

Questions to ask yourself

• How are we going to support this in production?
• How are we going to measure its adoption?
• How are we going to debug this?
• What are the metrics I should take care of?
• ...

[mergify]

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

• backport-v./d./d./d is the label to automatically backport to the 8./d branch. /d is the digit

NOTE: backport-skip has been added to this pull request.

[elasticmachine]

💔 Tests Failed

the below badges are clickable and redirect to their specific view in the CI or DOCS

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Build stats

• Start Time: 2023-08-29T13:00:18.665+0000

• Duration: 29 min 22 sec

Test stats 🧪

Test	Results
Failed	1
Passed	6216
Skipped	47
Total	6264

Test errors

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Test / Matrix - PLATFORM = 'windows-2016 && windows-immutable' / Test / TestRemovePath – github.com/elastic/elastic-agent/internal/pkg/agent/install

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 Failed 

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 === RUN   TestRemovePath
    uninstall_windows_test.go:54: 
        	Error Trace:	C:/Users/jenkins/workspace/_agent_elastic-agent-mbp_PR-3314/src/github.com/elastic/elastic-agent/internal/pkg/agent/install/uninstall_windows_test.go:54
        	Error:      	Received unexpected error:
        	            	could not remove "C:\\Users\\jenkins\\AppData\\Local\\Temp\\TestRemovePath3660284283\\001\\subdir", unretriable error: failed to open handle after rename for "C:\\Users\\jenkins\\AppData\\Local\\Temp\\TestRemovePath3660284283\\001\\subdir\\main.exe": The process cannot access the file because it is being used by another process.
        	Test:       	TestRemovePath
--- FAIL: TestRemovePath (1.99s)
 

Steps errors

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Go unitTest

• Took 9 min 56 sec . View more details here
• Description: mage unitTest

Checks if running on a Unix-like node

• Took 0 min 0 sec . View more details here
• Description: script returned exit code 1

🐛 Flaky test report

❕ There are test failures but not known flaky tests.

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Genuine test errors

💔 There are test failures but not known flaky tests, most likely a genuine test failure.

• Name: Test / Matrix - PLATFORM = 'windows-2016 && windows-immutable' / Test / TestRemovePath – github.com/elastic/elastic-agent/internal/pkg/agent/install

🤖 GitHub comments

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[elasticmachine]

🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	98.765% (80/81)	👍
Files	67.368% (192/285)	👍
Classes	66.105% (353/534)	👍
Methods	52.921% (1105/2088)	👍 0.025
Lines	38.529% (12609/32726)	👎 -0.006
Conditionals	100.0% (0/0)	💚

[cmacknz]

Test failures are unrelated, merging.