ci: detect apk usage generally

Rather than listing image names, which makes it less easy to
run custom CI jobs.

ci/test/01_base_install.sh

@@ -37,7 +37,7 @@ if [ -n "${APT_LLVM_V}" ]; then
   )
 fi
 
-if [[ $CI_IMAGE_NAME_TAG == *alpine* ]]; then
+if command -v apk >/dev/null 2>&1; then
   ${CI_RETRY_EXE} apk update
   # shellcheck disable=SC2086
   ${CI_RETRY_EXE} apk add --no-cache $CI_BASE_PACKAGES $PACKAGES