ci: bump cosaPod memory requirement to 5Gi

We're hitting memory limits when running the reprovisioning tests. We
should investigate why we need 1Gi of overhead, but for now to get
unblocked let's just bump it.

.cci.jenkinsfile

@@ -41,8 +41,8 @@ stage("Build") {
 }
 
 // Build FCOS and run kola tests.
-// Both kola and kolaTestIso require 4G max. Add 512M for overhead.
-cosaPod(runAsUser: 0, memory: "4608Mi", cpu: "4") {
+// Both kola and kolaTestIso require 4G max. Add 1G for overhead.
+cosaPod(runAsUser: 0, memory: "5Gi", cpu: "4") {
   stage("Build FCOS") {
     checkout scm
     unstash 'build'