Test against 8.10 on main with the 8.11 agent by editing the package version

[cmacknz]

The same as https://github.com/elastic/elastic-agent/pull/3276/files but with the package version file edit moved to happen in the right place.

Also fixes a bug in the GetPrevMinor() method of our version parser package. We need to keep this change.

I hope we get an 8.11 snapshot soon and we don't need this, but if we don't we'll merge it and then revert once the 8.11 snapshot is ready and work on less ugly solution for the next time this happens.

[elasticmachine]

Pinging @elastic/elastic-agent (Team:Elastic-Agent)

[elasticmachine]

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• Start Time: 2023-08-23T00:49:46.292+0000

• Duration: 38 min 39 sec

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Test	Results
Failed	0
Passed	6305
Skipped	47
Total	6352

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[elasticmachine]

🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	98.75% (79/80)	👍
Files	67.832% (194/286)	👍
Classes	66.292% (354/534)	👍
Methods	52.944% (1106/2089)	👍 0.07
Lines	38.662% (12653/32727)	👍 0.014
Conditionals	100.0% (0/0)	💚

[cmacknz]

The GetPrevMinor method was discarding the prerelease and build metadata information.

[cmacknz]

Looks like we need to fix the upgrade tests to respect the test stack version:

    fixture.go:433: >> running agent with: [/opt/Elastic/Agent/elastic-agent upgrade 8.11.0-SNAPSHOT --source-uri file:///home/ubuntu/agent/.agent-testing/local --skip-verify]
    upgrade_test.go:469: 
        	Error Trace:	/home/ubuntu/agent/testing/integration/upgrade_test.go:469
        	            				/home/ubuntu/agent/testing/integration/upgrade_test.go:215
        	Error:      	Received unexpected error:
        	            	exit status 1
        	Test:       	TestStandaloneUpgrade/Upgrade_8.10.0_to_8.11.0-SNAPSHOT
        	Messages:   	error triggering agent upgrade to version "8.11.0-SNAPSHOT", output:

This just keeps getting uglier...

[AndersonQ]

@cmacknz with @pchila's help I took another approach and just needed to set AGENT_PACKAGE_VERSION, AGENT_STACK_VERSION and AGENT_VERSION when building the agent and running the tests on buildkite to have it working. I've also merged you fix on the version package on my PR #3276.

I think we can close this one and finish the review and any last change there.

[cmacknz]

Yes that solution is much nicer, closing this one.