Remove default profile during environment merge

This change fixes a minor bug with the implementation of
ConfigurableEnvironment#merge, introduced in SPR-9444. During a merge
of two environments A and B, where A has default profiles [prod] and B
has default profiles [default] (the so-called 'reserved default
profile'), B would complete the merge process having a collection of
profiles reading [default, prod], which is incorrect.

This commit explicitly ensure's that B's reserved default profile is
removed if A has a set of default profiles greater than zero. If A
consists only of [default], B will inherit it during the merge
correctly; if A consists of [p1, p2], B will result in [p1, p2] as
well; if B consists of [p1] and A of [p2, p3], B will result in
[p1, p2, p3] post-merge.

Issue: SPR-9761, SPR-9444

spring-core/src/main/java/org/springframework/core/env/AbstractEnvironment.java

@@ -409,8 +409,11 @@ public abstract class AbstractEnvironment implements ConfigurableEnvironment {
 		for (String profile : parent.getActiveProfiles()) {
 			this.activeProfiles.add(profile);
 		}
-		for (String profile : parent.getDefaultProfiles()) {
-			this.defaultProfiles.add(profile);
+		if (parent.getDefaultProfiles().length > 0) {
+			this.defaultProfiles.remove(RESERVED_DEFAULT_PROFILE_NAME);
+			for (String profile : parent.getDefaultProfiles()) {
+				this.defaultProfiles.add(profile);
+			}
 		}
 	}