Use RHEL 8 to test old server versions (#1700)

Author: alcaeus

.evergreen/config/build-variants.yml

@@ -16,18 +16,6 @@ buildvariants:
     run_on: debian11-small
     tasks:
       - name: "build-all-php"
-  - name: build-debian10
-    display_name: "Build: Debian 10"
-    tags: ["build", "debian", "x64", "pr", "tag"]
-    run_on: debian10-small
-    tasks:
-      - name: "build-all-php"
-  - name: build-debian92
-    display_name: "Build: Debian 9.2"
-    tags: ["build", "debian", "x64", "pr", "tag"]
-    run_on: debian92-small
-    tasks:
-      - name: "build-all-php"
 
   # RHEL
   - name: build-rhel90

.evergreen/config/generated/test-variant/legacy-php-full.yml

@@ -36,15 +36,15 @@
           - ".ocsp .5.0"
 
   # Test versions < 5.0
-  - name: test-debian92-php-%phpVersion%
-    tags: ["test", "debian", "x64", "php%phpVersion%", "pr", "tag"]
-    display_name: "Test: Debian 9.2, PHP %phpVersion%"
-    run_on: debian92-small
+  - name: test-rhel80-php-%phpVersion%
+    tags: ["test", "rhel", "x64", "php%phpVersion%", "pr", "tag"]
+    display_name: "Test: RHEL 8.0, PHP %phpVersion%"
+    run_on: rhel80-small
     expansions:
-      FETCH_BUILD_VARIANT: "build-debian92"
+      FETCH_BUILD_VARIANT: "build-rhel8"
       FETCH_BUILD_TASK: "build-php-%phpVersion%"
     depends_on:
-      - variant: "build-debian92"
+      - variant: "build-rhel8"
         name: "build-php-%phpVersion%"
     tasks:
       # Remember to add new major versions here as they are released

.evergreen/config/generated/test-variant/modern-php-full.yml

@@ -57,15 +57,15 @@
           - ".ocsp .5.0"
 
   # Test versions < 5.0
-  - name: test-debian92-php-%phpVersion%
-    tags: ["test", "debian", "x64", "php%phpVersion%", "pr", "tag"]
-    display_name: "Test: Debian 9.2, PHP %phpVersion%"
-    run_on: debian92-small
+  - name: test-rhel80-php-%phpVersion%
+    tags: ["test", "rhel", "x64", "php%phpVersion%", "pr", "tag"]
+    display_name: "Test: RHEL 8.0, PHP %phpVersion%"
+    run_on: rhel80-small
     expansions:
-      FETCH_BUILD_VARIANT: "build-debian92"
+      FETCH_BUILD_VARIANT: "build-rhel8"
       FETCH_BUILD_TASK: "build-php-%phpVersion%"
     depends_on:
-      - variant: "build-debian92"
+      - variant: "build-rhel8"
         name: "build-php-%phpVersion%"
     tasks:
       # Remember to add new major versions here as they are released