Move Linux "stress" tests to autoscaled instances

The autoscaling GitLab CI runners currently used for most GitLab CI jobs
spin up AWS EC2 instances that are at least as powerful as the dedicated
instances used for running "stress" tests.  Move all Linux-based
"stress" tests to autoscaling GitLab CI runners to enable deprovisioning
Linux AWS instances reserved for running "stress" tests.  Leave FreeBSD
"stress" tests intact as there is currently no support for autoscaling
BSD instances.

.gitlab-ci.yml

@@ -90,7 +90,7 @@ stages:
     - ovh
     - amd64
 
-# Autoscaling GitLab Runner on AWS EC2
+# Autoscaling GitLab Runner on AWS EC2 (amd64)
 
 .linux-amd64: &linux_amd64
   tags:
@@ -99,21 +99,16 @@ stages:
     - runner-manager
     - amd64
 
-# Stress-testing runners
+# Autoscaling GitLab Runner on AWS EC2 (arm64)
 
-.linux-stress-amd64: &linux_stress_amd64
+.linux-arm64: &linux_arm64
   tags:
-    - amd64
+    - linux
     - aws
-    - linux-stress
-    - stress
-
-.linux-stress-arm64: &linux_stress_arm64
-  tags:
+    - runner-manager
     - aarch64
-    - aws
-    - linux-stress
-    - stress
+
+# Stress-testing runners
 
 .freebsd-stress-amd64: &freebsd_stress_amd64
   tags:
@@ -192,7 +187,7 @@ stages:
 
 .fedora-38-arm64: &fedora_38_arm64_image
   image: "$CI_REGISTRY_IMAGE:fedora-38-arm64"
-  <<: *linux_stress_arm64
+  <<: *linux_arm64
 
 # Ubuntu
 
@@ -1562,7 +1557,7 @@ respdiff-long-third-party:
 
 stress:authoritative:fedora:38:amd64:
   <<: *fedora_38_amd64_image
-  <<: *linux_stress_amd64
+  <<: *linux_amd64
   <<: *stress_job
   variables:
     CC: gcc
@@ -1577,7 +1572,7 @@ stress:authoritative:fedora:38:amd64:
 
 stress:recursive:fedora:38:amd64:
   <<: *fedora_38_amd64_image
-  <<: *linux_stress_amd64
+  <<: *linux_amd64
   <<: *stress_job
   variables:
     CC: gcc
@@ -1592,7 +1587,7 @@ stress:recursive:fedora:38:amd64:
 
 stress:rpz:fedora:38:amd64:
   <<: *fedora_38_amd64_image
-  <<: *linux_stress_amd64
+  <<: *linux_amd64
   <<: *stress_job
   variables:
     CC: gcc
@@ -1607,7 +1602,7 @@ stress:rpz:fedora:38:amd64:
 
 stress:authoritative:fedora:38:arm64:
   <<: *fedora_38_arm64_image
-  <<: *linux_stress_arm64
+  <<: *linux_arm64
   <<: *stress_job
   variables:
     CC: gcc
@@ -1622,7 +1617,7 @@ stress:authoritative:fedora:38:arm64:
 
 stress:recursive:fedora:38:arm64:
   <<: *fedora_38_arm64_image
-  <<: *linux_stress_arm64
+  <<: *linux_arm64
   <<: *stress_job
   variables:
     CC: gcc
@@ -1637,7 +1632,7 @@ stress:recursive:fedora:38:arm64:
 
 stress:rpz:fedora:38:arm64:
   <<: *fedora_38_arm64_image
-  <<: *linux_stress_arm64
+  <<: *linux_arm64
   <<: *stress_job
   variables:
     CC: gcc