perf: enable go caching and install task from prebuilt binary

Every job that uses this action paid several minutes of avoidable setup.

actions/setup-go was invoked with `cache: false`, so each job re-downloaded
the whole module graph and recompiled every dependency from scratch. On
mcvs-scanner this accounted for roughly 190-300s per job before the first
test line was even printed.

The version guard around the Task install had also been silently broken
since Task 3.44: it matched `Task version: v<x>`, but Task now reports a
bare `<x>`. The guard therefore never matched and every job unconditionally
recompiled Task from source, costing ~90s each. The guard now matches the
bare version, which covers both the old and new output formats, and the
prebuilt binary is installed instead of compiling from source, mirroring how
golangci-lint is already installed in build/task.yml.

Coverage results are unaffected: the coverage task already passes -count=1
(#344), so a warm build cache cannot cause cached test results to be
reported as coverage.

Author: Joeri-Abbo

action.yml

@@ -104,7 +104,7 @@ runs:
         inputs.testing-type == 'unit'
       with:
         go-version-file: ${{ inputs.go-version-file }}
-        cache: false
+        cache: true
     - name: install task
       if: |
         inputs.release-dir != '' ||
@@ -121,9 +121,23 @@ runs:
         inputs.testing-type == 'unit'
       shell: bash
       run: |
-        if ! task --version | grep -q "Task version: v${{ inputs.task-version }}"; then
-          major_version=$(echo "${{ inputs.task-version }}" | sed -E 's/^([0-9]+).*/\1/')
-          go install github.com/go-task/task/v${major_version}/cmd/task@v${{ inputs.task-version }}
+        # Task <= 3.38 reported 'Task version: v3.38.0 (h1:...)', whereas newer
+        # releases report a bare '3.51.1'. Matching the bare version covers
+        # both, so that an already installed Task is actually detected.
+        if ! task --version 2>/dev/null | grep -qF "${{ inputs.task-version }}"; then
+          # The prebuilt binary is used rather than 'go install', which compiles
+          # Task from source and costs roughly 90s in every job. This mirrors
+          # how golangci-lint is installed in build/task.yml.
+          #
+          # The destination mirrors what 'go install' would have used, so that
+          # Task still lands on a directory that is already on the PATH.
+          bindir="$(go env GOBIN)"
+          if [ -z "${bindir}" ]; then
+            bindir="$(go env GOPATH)/bin"
+          fi
+          curl \
+            -sSfL https://raw.githubusercontent.com/go-task/task/main/install-task.sh |\
+            sh -s -- -b "${bindir}" v${{ inputs.task-version }}
         fi
 
         echo "verifying that task can be found and run..."