build: configure onDemand for release-please

Author: chingor13

.github/release-please.yml

@@ -2,20 +2,29 @@ primaryBranch: main
 releaseType: java-yoshi
 manifest: true
 handleGHRelease: true
+onDemand: true
 branches:
     - branch: 1.0.x
       releaseType: java-backport
       bumpMinorPreMajor: true
+      onDemand: true
     - branch: 1.13.x
       releaseType: java-backport
+      onDemand: true
     - branch: 1.25.x
       releaseType: java-backport
+      onDemand: true
     - branch: 1.37.x
       releaseType: java-backport
+      onDemand: true
     - branch: 1.53.x
       releaseType: java-backport
+      onDemand: true
     - branch: 1.61.x
       releaseType: java-backport
+      onDemand: true
     - branch: 1.58.x
       releaseType: java-backport
+      onDemand: true
     - branch: protobuf-4.x-rc
+      onDemand: true