Use HTTPS for external links from XML files where possible

See gh-16311

spring-boot-tools/spring-boot-loader/src/it/executable-jar/src/main/assembly/jar-with-dependencies.xml

@@ -2,7 +2,7 @@
 <assembly
 	xmlns="http://maven.apache.org/plugins/maven-assembly-plugin/assembly/1.1.2"
 	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-	xsi:schemaLocation="http://maven.apache.org/plugins/maven-assembly-plugin/assembly/1.1.2 http://maven.apache.org/xsd/assembly-1.1.2.xsd">
+	xsi:schemaLocation="http://maven.apache.org/plugins/maven-assembly-plugin/assembly/1.1.2 https://maven.apache.org/xsd/assembly-1.1.2.xsd">
 	<id>full</id>
 	<formats>
 		<format>jar</format>

spring-boot-tools/spring-boot-loader/src/it/executable-props/src/main/assembly/jar-with-dependencies.xml

@@ -2,7 +2,7 @@
 <assembly
 	xmlns="http://maven.apache.org/plugins/maven-assembly-plugin/assembly/1.1.2"
 	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-	xsi:schemaLocation="http://maven.apache.org/plugins/maven-assembly-plugin/assembly/1.1.2 http://maven.apache.org/xsd/assembly-1.1.2.xsd">
+	xsi:schemaLocation="http://maven.apache.org/plugins/maven-assembly-plugin/assembly/1.1.2 https://maven.apache.org/xsd/assembly-1.1.2.xsd">
 	<id>full</id>
 	<formats>
 		<format>jar</format>

spring-boot-tools/spring-boot-loader/src/test/resources/root/META-INF/spring/application.xml

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <beans xmlns="http://www.springframework.org/schema/beans"
 	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
+	xsi:schemaLocation="http://www.springframework.org/schema/beans https://www.springframework.org/schema/beans/spring-beans.xsd">
 
 </beans>