Update GitLab CI to Alpine Linux 3.11

Since Alpine Linux 3.11 is the current Alpine Linux release, replace
Alpine Linux 3.10 GitLab CI jobs with their up-to-date counterparts.

.gitlab-ci.yml

@@ -67,8 +67,8 @@ stages:
 
 # Alpine Linux
 
-.alpine-3.10-amd64: &alpine_3_10_amd64_image
-  image: "$CI_REGISTRY_IMAGE:alpine-3.10-amd64"
+.alpine-3.11-amd64: &alpine_3_11_amd64_image
+  image: "$CI_REGISTRY_IMAGE:alpine-3.11-amd64"
   <<: *linux_amd64
 
 # CentOS
@@ -428,29 +428,29 @@ push:docs:sid:amd64:
     - master@isc-projects/bind9
     - /^v9_[1-9][0-9]$/@isc-projects/bind9
 
-# Jobs for regular GCC builds on Alpine Linux 3.10 (amd64)
+# Jobs for regular GCC builds on Alpine Linux 3.11 (amd64)
 
-gcc:alpine3.10:amd64:
+gcc:alpine3.11:amd64:
   variables:
     CC: gcc
     CFLAGS: "${CFLAGS_COMMON}"
     EXTRA_CONFIGURE: "--enable-dnstap"
-  <<: *alpine_3_10_amd64_image
+  <<: *alpine_3_11_amd64_image
   <<: *build_job
 
-system:gcc:alpine3.10:amd64:
-  <<: *alpine_3_10_amd64_image
+system:gcc:alpine3.11:amd64:
+  <<: *alpine_3_11_amd64_image
   <<: *system_test_job
   dependencies:
-    - gcc:alpine3.10:amd64
-  needs: ["gcc:alpine3.10:amd64"]
+    - gcc:alpine3.11:amd64
+  needs: ["gcc:alpine3.11:amd64"]
 
-unit:gcc:alpine3.10:amd64:
-  <<: *alpine_3_10_amd64_image
+unit:gcc:alpine3.11:amd64:
+  <<: *alpine_3_11_amd64_image
   <<: *unit_test_job
   dependencies:
-    - gcc:alpine3.10:amd64
-  needs: ["gcc:alpine3.10:amd64"]
+    - gcc:alpine3.11:amd64
+  needs: ["gcc:alpine3.11:amd64"]
 
 # Jobs for regular GCC builds on CentOS 6 (amd64)