GCLOUD: correction message strings for multiple changes affecting same label + type are partially dropped

[asn-iac]

Describe the bug
When multiple changes affect the same label + type in a GCLOUD zone, push/preview only displays one of the messages

To Reproduce
Steps to reproduce the behavior:

1. An existing dnsconfig and empty zones created in the GCLOUD account:

var DNS_GOOGLE = NewDnsProvider('gcloud');
D("dnscontrol-integration-test.com", REG_NONE,DnsProvider(DNS_GOOGLE),
	NAMESERVER_TTL('21600')
);

2. Modify the dnsconfig with changes that affect the same label + type:

var DNS_GOOGLE = NewDnsProvider('gcloud');
D("dnscontrol-integration-test.com", REG_NONE,DnsProvider(DNS_GOOGLE),
	NAMESERVER_TTL('21600'),
	MX('@', 10, 'mail.foo.bar.'),
	MX('@', 10, 'mail2.foo.bar.'),
	TXT('@', 'foo'),
	TXT('@', 'bar'),
	A('foo', '127.0.0.1'),
	A('foo', '127.0.0.2')
);

3. Run 'dnscontrol preview'

$ dnscontrol preview
******************** Domain: dnscontrol-integration-test.com
1 correction (gcloud)
#1: + CREATE MX dnscontrol-integration-test.com 10 mail2.foo.bar. ttl=300
+ CREATE TXT dnscontrol-integration-test.com "foo" ttl=300
+ CREATE A foo.dnscontrol-integration-test.com 127.0.0.2 ttl=300
Done. 1 corrections.

Expected behavior
Preview/Push should display all changes associated with a label

$ dnscontrol preview
******************** Domain: dnscontrol-integration-test.com
1 correction (gcloud)
#1: + CREATE MX dnscontrol-integration-test.com 10 mail.foo.bar. ttl=300
+ CREATE MX dnscontrol-integration-test.com 10 mail2.foo.bar. ttl=300
+ CREATE TXT dnscontrol-integration-test.com "bar" ttl=300
+ CREATE TXT dnscontrol-integration-test.com "foo" ttl=300
+ CREATE A foo.dnscontrol-integration-test.com 127.0.0.1 ttl=300
+ CREATE A foo.dnscontrol-integration-test.com 127.0.0.2 ttl=300
Done. 1 corrections.

DNS Provider

• GCLOUD

Additional context
The actual API changes are still read and executed correctly so the integration tests are passing. Will submit PR with fix for the messages.

[asn-iac]

PR #2759