ci: set TASK_CONCURRENCY=1 for Windows runners (#5185)

## Why
A couple races in practice:

> - Run 1 (codegen failed): race on
~/go/pkg/mod/cache/download/.../v0.2.2.partial during module download —
>    "Access is denied"
> - Run 2 (test-acc failed): race on
AppData\Local\go-build\...\gotestsum.exe during fork/exec — "file is
>   being used by another process"

Author: denik

.github/workflows/push.yml

@@ -88,6 +88,9 @@ jobs:
       id-token: write
       contents: read
 
+    env:
+      TASK_CONCURRENCY: ${{ matrix.os.name == 'windows' && '1' || '' }}
+
     strategy:
       fail-fast: false
       matrix:
@@ -228,6 +231,9 @@ jobs:
       id-token: write
       contents: read
 
+    env:
+      TASK_CONCURRENCY: ${{ matrix.os.name == 'windows' && '1' || '' }}
+
     strategy:
       fail-fast: false
       matrix:
@@ -277,6 +283,9 @@ jobs:
       id-token: write
       contents: read
 
+    env:
+      TASK_CONCURRENCY: ${{ matrix.os.name == 'windows' && '1' || '' }}
+
     strategy:
       fail-fast: false
       matrix: