Restore Git Credentials on NuttX repo

Something change on the GitHub side that has broken credentials
between the the fetch and buld workflow steps.  There is no
way to tell the checkout action to only re-auth so we have it
checkout the repo again, but it will use what it already has.

In the future we can change fetch step to just compute the
target refs and store them in a script that we can call to
set the environment variables for the targets much like
this patch.

Signed-off-by: Brennan Ashton <bashton@brennanashton.com>

.github/workflows/build.yml

@@ -162,13 +162,23 @@ jobs:
           retry_wait_seconds: 10
           command: docker pull docker.pkg.github.com/apache/incubator-nuttx-testing/nuttx-ci-linux
 
+      - name: Export NuttX Repo SHA
+        run:  echo "::set-env name=nuttx_sha::`git -C sources/nuttx rev-parse HEAD`"
+      - name: Refresh Git Credentials
+        uses: actions/checkout@v2
+        with:
+          repository: apache/incubator-nuttx
+          ref: ${{ env.nuttx_sha }}
+          path: sources/nuttx
+          fetch-depth: 1
+      - name: Get Tags for NuttX Repo
+        run: git -C sources/nuttx fetch --tags
       - name: Run builds
         uses: ./sources/testing/.github/actions/ci-container
         env:
           BLOBDIR: /tools/blobs
         with:
           run: |
-            git -C sources/nuttx fetch --tags
             cd sources/testing
             ./cibuild.sh -x testlist/${{matrix.boards}}.dat
 
@@ -207,8 +217,18 @@ jobs:
           path: prebuilt
           key: ${{ runner.os }}-tools-${{ hashFiles('./sources/testing/cibuild.sh') }}
 
+      - name: Export NuttX Repo SHA
+        run:  echo "::set-env name=nuttx_sha::`git -C sources/nuttx rev-parse HEAD`"
+      - name: Refresh Git Credentials
+        uses: actions/checkout@v2
+        with:
+          repository: apache/incubator-nuttx
+          ref: ${{ env.nuttx_sha }}
+          path: sources/nuttx
+          fetch-depth: 1
+      - name: Get Tags for NuttX Repo
+        run: git -C sources/nuttx fetch --tags
       - name: Run Builds
         run: |
-          git -C sources/nuttx fetch --tags
           cd sources/testing
           ./cibuild.sh -i -x testlist/${{matrix.boards}}.dat