Changed CI to just run on ubuntu-latest

If we already have to bump this version as GitHub phases out older
Ubuntu runners (which is reasonable), I don't really see the value of
pinning a specific version. We might as well just respond to any
broken dependencies caused by GitHub's implicit updates as they
happen...

It's not like CI is truly continuous.

.github/workflows/release.yml

@@ -11,7 +11,7 @@ defaults:
 
 jobs:
   release:
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-latest
 
     # need to manually check for a couple things
     # - tests passed?

.github/workflows/test.yml

@@ -12,7 +12,7 @@ env:
 jobs:
   # self-host test with littlefs-fuse
   test:
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
       - name: install
@@ -56,7 +56,7 @@ jobs:
 
   # test older versions
   test-lfs2_0:
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
       - name: install