Test on newer PPC architecture

Author: alcaeus

.evergreen/config/build-variants.yml

@@ -36,10 +36,10 @@ buildvariants:
     run_on: rhel82-arm64
     tasks:
       - name: "build-all-php"
-  - name: build-rhel8-power8
-    display_name: "Build: RHEL 8 Power8"
-    tags: ["build", "rhel", "power8", "tag"]
-    run_on: rhel8-power-large
+  - name: build-rhel9-power
+    display_name: "Build: RHEL 9 PPC"
+    tags: ["build", "rhel", "power", "tag"]
+    run_on: rhel9-power-small
     tasks:
       - name: "build-all-php"
   - name: build-rhel8