GitHub CI: update olegtarasov/get-tag to v2.1

v2 no longer works:

Error: Unable to process command '##[set-env name=GIT_TAG_NAME;]v0.5.5' successfully.
Error: The `set-env` command is disabled. Please upgrade to using Environment Files or opt into unsecure command execution by setting the `ACTIONS_ALLOW_UNSECURE_COMMANDS` environment variable to `true`. For more information see: https://github.blog/changelog/2020-10-01-github-actions-deprecating-set-env-and-add-path-commands/
Warning: The `set-output` command is deprecated and will be disabled soon. Please upgrade to using Environment Files. For more information see: https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/

Author: brechtm

.github/workflows/tests.yml

@@ -30,13 +30,13 @@ jobs:
           - NOXENV: check
           - NOXENV: check_docs
           - NOXENV: build_docs
-    env: ${{ matrix.env}}
+    env: ${{ matrix.env }}
     steps:
     - uses: actions/checkout@v3
       with:
         submodules: true
     - name: Get tag
-      uses: olegtarasov/get-tag@v2
+      uses: olegtarasov/get-tag@v2.1
     - name: Install Python ${{ env.current_python }}
       uses: actions/setup-python@v4
       with:
@@ -299,7 +299,7 @@ jobs:
       with:
         submodules: true
     - name: Get tag
-      uses: olegtarasov/get-tag@v2
+      uses: olegtarasov/get-tag@v2.1
     - name: Install Python ${{ env.current_python }}
       uses: actions/setup-python@v4
       with: