ci: increase FreeBSD VM memory to 2048MB

Intermittent CI failures without any useful diagnostics could be caused
by the OOM killer. 1024MB is not really enough to run 3 parallel jobs
with a modern C++ compiler.

.github/workflows/freebsd.yml

@@ -13,6 +13,7 @@ jobs:
     - name: Test in FreeBSD VM
       uses: vmactions/[email protected] # aka FreeBSD 13.0
       with:
+        mem: 2048
         usesh: true
         prepare: |
           export CPPFLAGS=-isystem/usr/local/include LDFLAGS=-L/usr/local/lib # sndio