Upgrade Spring Framework to 5.3.9

Closes gh-1894

Author: eleftherias

gradle/dependency-management.gradle

@@ -2,7 +2,7 @@ dependencyManagement {
 	imports {
 		mavenBom 'io.projectreactor:reactor-bom:2020.0.10'
 		mavenBom 'org.junit:junit-bom:5.7.1'
-		mavenBom 'org.springframework:spring-framework-bom:5.3.8'
+		mavenBom 'org.springframework:spring-framework-bom:5.3.9'
 		mavenBom 'org.springframework.data:spring-data-bom:2020.0.9'
 		mavenBom 'org.springframework.security:spring-security-bom:5.4.6'
 		mavenBom 'org.testcontainers:testcontainers-bom:1.15.3'