Update get-diff-action due to environment variables update (#993)

Github Actions changed the way they handle environment variables last week; the version of get-diff-action we were using used the old style.

Author: terriko

.github/workflows/pythonapp.yml

@@ -98,7 +98,7 @@ jobs:
         with:
           path: ~/.cache/cve-bin-tool
           key: ${{ runner.os }}-cve-bin-tool-${{ steps.get-date.outputs.date }}
-      - uses: technote-space/get-diff-action@v1
+      - uses: technote-space/get-diff-action@v4
         with:
           PREFIX_FILTER: |
             cve_bin_tool/checkers
@@ -197,4 +197,4 @@ jobs:
         run: >
           pytest -v
           test/test_cvedb.py
-          test/test_cli.py
+          test/test_cli.py