Use ubuntu 22 runners (#386)

Use ubuntu-22 runners for the valgrind, ASAN, and TSAN tests - to avoid
some strange new issue with ubuntu-20.
Generally it doesn't matter much where we run these memory fuzzers.

.github/workflows/build-test-cplusplus.yml

@@ -9,7 +9,7 @@ concurrency:
 jobs:
   valgrind:
     name: valgrind ubuntu
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     steps:
       - name: Checkout code
         uses: actions/checkout@v3
@@ -27,7 +27,7 @@ jobs:
 
   asan:
     name: ASAN ubuntu
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     steps:
       - name: Checkout code
         uses: actions/checkout@v3
@@ -48,7 +48,7 @@ jobs:
 
   tsan:
     name: TSAN ubuntu
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     steps:
       - name: Checkout code
         uses: actions/checkout@v3