Use Java 19 on CI. (#1485)

* Use Java 19 on CI.

* Use a variable.

* Attempt to fix syntax.

Author: colinrtwhite

.github/workflows/ci.yml

@@ -5,8 +5,8 @@ on:
             - main
     pull_request:
 env:
-    # Increment this to manually invalidate the cache.
-    CACHE_VERSION: 1
+    CACHE_VERSION: 1 # Increment this to invalidate the cache.
+    JAVA_VERSION: 19
 jobs:
     checks:
         name: Checks
@@ -17,7 +17,7 @@ jobs:
             - uses: actions/setup-java@v3
               with:
                   distribution: 'zulu'
-                  java-version: 17
+                  java-version: ${{ env.JAVA_VERSION }}
             - run: ./ci_clear_gradle_cache.sh
             - uses: actions/cache@v3
               with:
@@ -49,7 +49,7 @@ jobs:
             - uses: actions/setup-java@v3
               with:
                   distribution: 'zulu'
-                  java-version: 17
+                  java-version: ${{ env.JAVA_VERSION }}
             - run: ./ci_clear_gradle_cache.sh
             - uses: actions/cache@v3
               with:
@@ -75,7 +75,7 @@ jobs:
             - uses: actions/setup-java@v3
               with:
                   distribution: 'zulu'
-                  java-version: 17
+                  java-version: ${{ env.JAVA_VERSION }}
             - run: ./ci_clear_gradle_cache.sh
             - uses: actions/cache@v3
               with:
@@ -137,7 +137,7 @@ jobs:
             - uses: actions/setup-java@v3
               with:
                   distribution: 'zulu'
-                  java-version: 17
+                  java-version: ${{ env.JAVA_VERSION }}
             - run: ./ci_clear_gradle_cache.sh
             - uses: actions/cache@v3
               with: