Revert "Unskip the proxy URL tests. (#4321)" (#4337)

This reverts commit 5e17bc2.

Author: rdner

testing/integration/proxy_url_test.go

@@ -99,6 +99,7 @@ func TestProxyURL_EnrollProxyAndNoProxyInThePolicy(t *testing.T) {
 		Local: false,
 		Sudo:  true,
 	})
+	t.Skip("Flaky test: https://github.com/elastic/elastic-agent/issues/3154")
 
 	p := SetupTest(t)
 	t.Cleanup(func() {
@@ -146,6 +147,7 @@ func TestProxyURL_EnrollProxyAndEmptyProxyInThePolicy(t *testing.T) {
 		Local: false,
 		Sudo:  true,
 	})
+	t.Skip("Flaky test: https://github.com/elastic/elastic-agent/issues/3154")
 
 	p := SetupTest(t)
 	t.Cleanup(func() {
@@ -195,6 +197,7 @@ func TestProxyURL_ProxyInThePolicyTakesPrecedence(t *testing.T) {
 		Local: false,
 		Sudo:  true,
 	})
+	t.Skip("Flaky test: https://github.com/elastic/elastic-agent/issues/3154")
 
 	p := SetupTest(t)
 	t.Cleanup(func() {
@@ -258,6 +261,7 @@ func TestProxyURL_NoEnrollProxyAndProxyInThePolicy(t *testing.T) {
 		Local: false,
 		Sudo:  true,
 	})
+	t.Skip("Flaky test: https://github.com/elastic/elastic-agent/issues/3154")
 
 	p := SetupTest(t)
 	t.Cleanup(func() {
@@ -325,6 +329,7 @@ func TestProxyURL_RemoveProxyFromThePolicy(t *testing.T) {
 		Local: false,
 		Sudo:  true,
 	})
+	t.Skip("Flaky test: https://github.com/elastic/elastic-agent/issues/3154")
 
 	p := SetupTest(t)
 	t.Cleanup(func() {