Make compiler-rt version match the clang version in the gitea action

.gitea/workflows/validate.yaml

@@ -16,10 +16,9 @@ jobs:
           echo "http://dl-cdn.alpinelinux.org/alpine/edge/main" >> /etc/apk/repositories
           echo "http://dl-cdn.alpinelinux.org/alpine/edge/community" >> /etc/apk/repositories
 
-          # determine appropriate clang version
-          RT_VERSION=$(apk add --simulate compiler-rt | grep -o "compiler-rt-[0-9]*" | grep -o "[0-9]*")
-
+          # determine correct clang version and then install it
           apk update
+          RT_VERSION=$(apk add --simulate compiler-rt | grep -o "compiler-rt-[0-9]*" | grep -o "[0-9]*")
           apk add --no-cache llvm${RT_VERSION} clang${RT_VERSION} clang${RT_VERSION}-analyzer compiler-rt valgrind
 
           # Verify versions