GHA/checksrc: give more time for slow Azure servers [ci skip]

Sometimes 1 minutes is too short to install 39.4 kB of archives.

Ref: https://github.com/curl/curl/actions/runs/19898949860/job/57036965452

.github/workflows/checksrc.yml

@@ -122,7 +122,7 @@ jobs:
   xmllint:
     name: 'xmllint'
     runs-on: ubuntu-latest
-    timeout-minutes: 1
+    timeout-minutes: 3
     steps:
       - name: 'install prereqs'
         run: |