Use JDK 23 for generating Javadoc, too.

This brings us to the newest released version, which also means that it matches the version that we use for javac, so we require one less JDK.

cl/711811272 fixed [the error we'd previously been seeing with JDK 23](#6790 (comment)).

(Also, if someone has a JDK 23 already installed and skips our auto-downloading, use it even if it's not Temurin. I'd made this change for most toolchain usages in cl/711746683, but I missed the usage one for Javadoc.)

RELNOTES=n/a
PiperOrigin-RevId: 711829376

.github/workflows/ci.yml

@@ -40,14 +40,12 @@ jobs:
       # When we specify multiple JDKs, the final one becomes the default, which is used to execute Maven itself.
       # Our Maven configuration then specifies different JDKs to use for some of the steps:
       # - 11 (sometimes) to *download* to support anyone who runs JDiff or our Gradle integration tests (including our doc snapshots and our Java 11 CI test run) but not to use directly
-      # - 21 for building Javadoc
-      # - 23 for running javac (to help people who build Guava locally and might not use a recent JDK to run Maven)
+      # - 23 for running Javadoc and javac (to help people who build Guava locally and might not use a recent JDK to run Maven)
       - name: 'Set up JDKs'
         uses: actions/setup-java@8df1039502a15bceb9433410b1a100fbe190c53b # v4.5.0
         with:
           java-version: |
             ${{ matrix.java }}
-            21
             23
           distribution: 'temurin'
           cache: 'maven'
@@ -80,9 +78,7 @@ jobs:
         with:
           # For discussion, see the first setup-java block.
           # The publish-snapshot workflow doesn't run tests, so we don't have to care which version Maven would select for that step.
-          java-version: |
-            21
-            23
+          java-version: 23
           distribution: 'temurin'
           cache: 'maven'
       - name: 'Publish'
@@ -109,7 +105,6 @@ jobs:
           # But we need Java 11 for JDiff.
           java-version: |
             11
-            21
             23
           distribution: 'temurin'
           cache: 'maven'

android/pom.xml

@@ -199,20 +199,6 @@
             rm -rf ~/.m2/jdks/ ~/.m2/toolchains.xml
             (But don't run that if you have put something into ~/.m2/toolchains.xml yourself.)
             -->
-            <execution>
-              <id>download-21</id>
-              <goals>
-                <goal>toolchain</goal>
-              </goals>
-              <configuration>
-                <toolchains>
-                  <jdk>
-                    <version>21</version>
-                    <vendor>temurin</vendor>
-                  </jdk>
-                </toolchains>
-              </configuration>
-            </execution>
             <execution>
               <id>download-23-and-surefire-version</id>
               <goals>
@@ -329,8 +315,7 @@
           <version>3.11.2</version>
           <configuration>
             <jdkToolchain>
-              <version>21</version>
-              <vendor>temurin</vendor>
+              <version>23</version>
             </jdkToolchain>
             <quiet>true</quiet>
             <notimestamp>true</notimestamp>

pom.xml

@@ -200,20 +200,6 @@
             rm -rf ~/.m2/jdks/ ~/.m2/toolchains.xml
             (But don't run that if you have put something into ~/.m2/toolchains.xml yourself.)
             -->
-            <execution>
-              <id>download-21</id>
-              <goals>
-                <goal>toolchain</goal>
-              </goals>
-              <configuration>
-                <toolchains>
-                  <jdk>
-                    <version>21</version>
-                    <vendor>temurin</vendor>
-                  </jdk>
-                </toolchains>
-              </configuration>
-            </execution>
             <execution>
               <id>download-23-and-surefire-version</id>
               <goals>
@@ -324,8 +310,7 @@
           <version>3.11.2</version>
           <configuration>
             <jdkToolchain>
-              <version>21</version>
-              <vendor>temurin</vendor>
+              <version>23</version>
             </jdkToolchain>
             <quiet>true</quiet>
             <notimestamp>true</notimestamp>