Give the ARM cross-compile job's build step its own time limit

apt on the runner mirror sometimes crawls for minutes
(actions/runner-images#14823), and the cross compiler is large enough
that its install alone used up the job's 10-minute limit. Loosen the job
limit to 30 minutes and limit the build step, which normally takes a few
seconds, to 2 minutes.

.github/workflows/test-32bit.yml

diff --git a/.github/workflows/test-32bit.yml b/.github/workflows/test-32bit.yml
index 45d3393..347a90c 100644
--- a/.github/workflows/test-32bit.yml
+++ b/.github/workflows/test-32bit.yml
@@ -28,10 +28,13 @@
   test-arm32:
     name: ARM 32-bit (cross-compile)
     runs-on: ubuntu-latest
-    timeout-minutes: 10
+    # Loose, because apt on the runner mirror can crawl for minutes; the build
+    # step has its own tight limit.
+    timeout-minutes: 30
     steps:
       - uses: actions/checkout@v4
       - name: Install cross compiler
         run: sudo apt-get update && sudo apt-get install -y g++-arm-linux-gnueabihf
       - name: Build (ARM 32-bit)
+        timeout-minutes: 2
         run: arm-linux-gnueabihf-g++ -std=c++11 -Wall -Wextra -Wno-psabi -Werror -c -o /dev/null test/test_32bit_build.cpp