[8.x] Change backwards test configuration to use trial license (#115226) (#115244)

* Change backwards test configuration to use trial license (#115226)

* Change backwards test configuration to use trial license

* unmute

(cherry picked from commit 5e761fe)

# Conflicts:
#	muted-tests.yml

* Update muted-tests.yml

Author: kkrik-es

qa/mixed-cluster/build.gradle

@@ -71,6 +71,7 @@ BuildParams.bwcVersions.withWireCompatible { bwcVersion, baseName ->
       numberOfNodes = 4
       setting 'path.repo', "${buildDir}/cluster/shared/repo/${baseName}"
       setting 'xpack.security.enabled', 'false'
+      setting "xpack.license.self_generated.type", "trial"
       /* There is a chance we have more master changes than "normal", so to avoid this test from failing,
        we increase the threshold (as this purpose of this test isn't to test that specific indicator). */
       if (bwcVersion.onOrAfter(Version.fromString("8.4.0"))) {