GHA: switch 12 Linux jobs to arm64

More cost-effective and seems as fast or faster than Intel.

In particular, valgrind seems to be almost 2x fast. So fast the job pair
could fit under 10 minutes if merged again (but would be the longest in
GHA/Linux.)

Installing packages is slightly slower. The package repo is Ubuntu's
which is slower than the Azure mirror used on Intel (unless Azure is
broken, which happened a lot last year).

To add to more jobs, the locally built deps also need to be migrated.

Also:
- add workaround for failing sshd server on Linux arm runners, caused by
  world-writable `HOME` directory.

Closes #20231

.github/workflows/checkdocs.yml

@@ -118,7 +118,7 @@ jobs:
 
   badwords-synopsis:
     name: 'badwords, synopsis'
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-24.04-arm
     steps:
       - uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6.0.1
         with:
@@ -132,7 +132,7 @@ jobs:
 
   man-examples:
     name: 'man-examples'
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-24.04-arm
     steps:
       - uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6.0.1
         with: