Use version-spring-boot attribute to reference Spring Boot's version

Closes gh-46187

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/docs/antora/modules/gradle-plugin/examples/getting-started/apply-plugin-commercial.gradle

@@ -15,5 +15,5 @@
  */
 
 plugins {
-	id 'org.springframework.boot' version '{gradle-project-version}'
+	id 'org.springframework.boot' version '{version-spring-boot}'
 }

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/docs/antora/modules/gradle-plugin/examples/getting-started/apply-plugin-commercial.gradle.kts

@@ -1,3 +1,3 @@
 plugins {
-	id("org.springframework.boot") version "{gradle-project-version}"
+	id("org.springframework.boot") version "{version-spring-boot}"
 }

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/docs/antora/modules/gradle-plugin/examples/managing-dependencies/depend-on-plugin-commercial.gradle

@@ -15,5 +15,5 @@
  */
 
 plugins {
-	id 'org.springframework.boot' version '{gradle-project-version}' apply false
+	id 'org.springframework.boot' version '{version-spring-boot}' apply false
 }

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/docs/antora/modules/gradle-plugin/examples/managing-dependencies/depend-on-plugin-commercial.gradle.kts

@@ -1,3 +1,3 @@
 plugins {
-	id("org.springframework.boot") version "{gradle-project-version}" apply false
+	id("org.springframework.boot") version "{version-spring-boot}" apply false
 }