Add Maven matrix testing

* Use 's4u/setup-maven-action' GH action to test Maven compatibility matrix
* Defined formal Maven compatible version (1-year-old + most recent minor)

Fixes #630

.github/workflows/build.yaml

@@ -22,28 +22,27 @@ jobs:
       fail-fast: false
       max-parallel: 4
       matrix:
-        java:
-          - 8
-          - 11
-          - 17
         os:
           - ubuntu-latest
           - windows-latest
           - macos-latest
+        java:
+          - 8
+          - 11
+          - 17
+        # 1-year-old version + latest minor
+        maven:
+          - 3.8.5
+          - 3.8.8
+          - 3.9.1
     runs-on: ${{ matrix.os }}
     steps:
-      - uses: actions/checkout@v3
+      - uses: s4u/setup-maven-action@v1.7.0
         with:
-          fetch-depth: 1
-      - uses: actions/setup-java@v3
-        with:
-          distribution: 'temurin'
+          java-distribution: 'temurin'
           java-version: ${{ matrix.java }}
-      - name: Cache dependencies
-        uses: actions/cache@v2
-        with:
-          path: ~/.m2/repository
-          key: ${{ runner.os }}-mvn-cache-${{ hashFiles('**/pom.xml') }}
-          restore-keys: ${{ runner.os }}-mvn-cache-
-      - name: Build
-        run: ./mvnw -B -V -Prun-its clean verify
+          maven-version: ${{ matrix.maven }}
+      - name: Maven version
+        run: mvn -version
+      - name: Build & Test
+        run: mvn -B -Prun-its clean verify

README.adoc

@@ -116,6 +116,11 @@ These are the minimal steps to convert your AsciiDoc documents to HTML with the
 
 You can find examples ready to copy-paste in the {uri-examples}[Asciidoctor Maven examples] project.
 
+== Maven compatible versions
+
+// 1-year-old versions + most recent minor
+asciidoctor-maven-plugin supports Maven 3.8.5+ and 3.9.x versions.
+
 == Contributing
 
 This plugin is an open source project made possible with the help of users and enthusiasts.

docs/modules/plugin/pages/compatibility-matrix.adoc

@@ -1,9 +1,18 @@
 = Compatibility Matrix
 
 Here is the list of supported versions alongside the required {uri-asciidoctorj}[AsciidoctorJ] version.
-Release candidate releases are not accounted. 
+Release candidate releases are not accounted.
 
-== Versions
+== Maven compatible versions
+
+The current policy for Maven compatibility is to support https://maven.apache.org/docs/history.html[1-year-old releases and the most recent minor].
+
+That is:
+
+* Maven v3.8.5 and higher
+* Maven v3.9.x
+
+== AsciidoctorJ compatible versions
 
 |===
 |Asciidoctor Maven Plugin | AsciidoctorJ | Supported