try to reduce the path length on windows ci

.github/workflows/windows-build.yml

@@ -99,8 +99,16 @@ jobs:
 
     - name: Install nimble deps
       if: steps.cache-nimbledeps.outputs.cache-hit != 'true'
+      env:
+        # lsquic bundles BoringSSL as a submodule whose fuzz corpus has deeply-nested
+        # paths. With the default TEMP at D:\a\_temp\msys64\tmp the total path length
+        # exceeds Windows MAX_PATH (260 chars). Use a short TEMP so nimble's scratch
+        # directory stays within the limit.
+        TEMP: 'C:\t'
+        TMP: 'C:\t'
       run: |
         export PATH="$GITHUB_WORKSPACE/.nim_runtime/bin:$HOME/.nimble/bin:$PATH"
+        mkdir -p /c/t
         nimble setup --localdeps -y
         make rebuild-nat-libs-nimbledeps CC=gcc
         make rebuild-bearssl-nimbledeps CC=gcc