[Tests] Include maintenance in BwC unreleased versions

We don't support upgrades between versions further than 1 major.
This change filters out these versions (e.g., 7.x from 9.x branches)
from being used by BwC tests. It is necessary to correctly calculate the
 maintained versions from the perspective of the current branch.

Author: jozala

build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/BwcVersions.java

@@ -162,6 +162,7 @@ private Map<Version, UnreleasedVersionInfo> computeUnreleased(List<String> devel
         // Now handle all the feature freeze branches
         List<String> featureFreezeBranches = developmentBranches.stream()
             .filter(b -> Pattern.matches("[0-9]+\\.[0-9]+", b))
+            .filter(b -> currentVersion.getMajor() - Version.fromString(b, Version.Mode.RELAXED).getMajor() <= 1)
             .sorted(reverseOrder(comparing(s -> Version.fromString(s, Version.Mode.RELAXED))))
             .toList();
 

build-tools-internal/src/test/groovy/org/elasticsearch/gradle/internal/BwcVersionsSpec.groovy

@@ -37,7 +37,7 @@ class BwcVersionsSpec extends Specification {
 
         then:
         unreleased == [
-            (v('8.15.2')): new UnreleasedVersionInfo(v('8.15.2'), '8.15', ':distribution:bwc:bugfix2'),
+            (v('8.15.2')): new UnreleasedVersionInfo(v('8.15.2'), '8.15', ':distribution:bwc:maintenance'),
             (v('8.16.1')): new UnreleasedVersionInfo(v('8.16.1'), '8.16', ':distribution:bwc:bugfix'),
             (v('8.17.0')): new UnreleasedVersionInfo(v('8.17.0'), '8.x', ':distribution:bwc:minor'),
             (v('9.0.0')): new UnreleasedVersionInfo(v('9.0.0'), 'main', ':distribution'),
@@ -67,7 +67,7 @@ class BwcVersionsSpec extends Specification {
 
         then:
         unreleased == [
-            (v('8.15.2')): new UnreleasedVersionInfo(v('8.15.2'), '8.15', ':distribution:bwc:bugfix2'),
+            (v('8.15.2')): new UnreleasedVersionInfo(v('8.15.2'), '8.15', ':distribution:bwc:maintenance'),
             (v('8.16.1')): new UnreleasedVersionInfo(v('8.16.1'), '8.16', ':distribution:bwc:bugfix'),
             (v('8.17.0')): new UnreleasedVersionInfo(v('8.17.0'), '8.17', ':distribution:bwc:staged'),
             (v('8.18.0')): new UnreleasedVersionInfo(v('8.18.0'), '8.x', ':distribution:bwc:minor'),
@@ -99,7 +99,7 @@ class BwcVersionsSpec extends Specification {
 
         then:
         unreleased == [
-            (v('8.16.2')): new UnreleasedVersionInfo(v('8.16.2'), '8.16', ':distribution:bwc:bugfix2'),
+            (v('8.16.2')): new UnreleasedVersionInfo(v('8.16.2'), '8.16', ':distribution:bwc:maintenance'),
             (v('8.17.1')): new UnreleasedVersionInfo(v('8.17.1'), '8.17', ':distribution:bwc:bugfix'),
             (v('8.18.0')): new UnreleasedVersionInfo(v('8.18.0'), '8.18', ':distribution:bwc:staged2'),
             (v('8.19.0')): new UnreleasedVersionInfo(v('8.19.0'), '8.x', ':distribution:bwc:minor'),