Fix selection of testing version (#6578)

* mark and skip flaky TestOTelManager_Run

* updated test version selection

* Update testing/upgradetest/versions.go

Co-authored-by: Craig MacKenzie <craig.mackenzie@elastic.co>

* updated versions

* pin 9.0

* pin 9.0

* removed version pin for 9.0

* Update magefile.go

* updated branches

* fix previousMinor for pinned 9.0

---------

Co-authored-by: Craig MacKenzie <craig.mackenzie@elastic.co>
Co-authored-by: Panos Koutsovasilis <panos.koutsovasilis@elastic.co>

testing/integration/testdata/.upgrade-test-agent-versions.yml

@@ -5,8 +5,8 @@
 # upgrade integration tests.
 
 testVersions:
+  - 9.0.0-SNAPSHOT
   - 8.19.0-SNAPSHOT
-  - 8.18.0-SNAPSHOT
   - 8.17.2
   - 8.16.4
   - 7.17.28-SNAPSHOT

testing/upgradetest/versions.go

@@ -188,6 +188,7 @@ func findRequiredVersions(sortedParsedVersions []*version.ParsedSemVer, reqs Ver
 	currentMajor := parsedUpgradeToVersion.Major()
 	currentMinor := parsedUpgradeToVersion.Minor()
 
+	skipCurrentMajor := false
 	currentMajorsToFind := reqs.CurrentMajors
 	previousMajorsToFind := reqs.PreviousMajors
 	previousMinorsToFind := reqs.PreviousMinors
@@ -214,15 +215,18 @@ func findRequiredVersions(sortedParsedVersions []*version.ParsedSemVer, reqs Ver
 			currentMajorsToFind-- // counts as the current major as well
 
 		// current majors
-		case currentMajorsToFind > 0 && version.Major() == currentMajor:
+		case currentMajorsToFind > 0 && version.Major() == currentMajor && !skipCurrentMajor:
 			upgradableVersions = append(upgradableVersions, version.String())
 			currentMajorsToFind--
 
 		// previous majors
 		case previousMajorsToFind > 0 && version.Major() < currentMajor:
 			upgradableVersions = append(upgradableVersions, version.String())
 			currentMajor = version.Major()
+			currentMinor = version.Minor()
 			previousMajorsToFind--
+			previousMinorsToFind-- // count as prev minor as well
+			skipCurrentMajor = true
 
 		// since the list is sorted we can stop here
 		default:
@@ -252,7 +256,13 @@ func PreviousMinor() (*version.ParsedSemVer, error) {
 		// will only contain minors from the previous major (vX-1). Further, since the
 		// version list is sorted in descending order (newer versions first), we can return the
 		// first item from the list as it will be the newest minor of the previous major.
-		return versions[0], nil
+		for _, v := range versions {
+			if v.Less(*current) {
+				return v, nil
+			}
+		}
+
+		return nil, ErrNoPreviousMinor
 	}
 
 	for _, v := range versions {