Revert "TO-DROP: clone build-extra from dscho/please-sh-tolerate-missing-sparse"

This reverts commit 075a9ad.

The build-extra changes that this commit was waiting on
(git-for-windows/build-extra#710) have
landed on `git-for-windows/build-extra` `main`, so the workflows
can go back to cloning the upstream branch.

Assisted-by: Opus 4.7
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

.github/workflows/check-for-missing-dlls.yml

@@ -29,11 +29,7 @@ jobs:
         env:
           REF: ${{github.ref}}
       - name: clone build-extra
-        shell: bash
-        run: |
-          git clone --depth=1 --single-branch \
-            -b please-sh-tolerate-missing-sparse \
-            https://github.com/dscho/build-extra
+        run: git clone --depth=1 --single-branch -b main https://github.com/git-for-windows/build-extra
       - name: create build-installers artifact
         shell: bash
         run: |

.github/workflows/ci-artifacts.yml

@@ -30,11 +30,7 @@ jobs:
           git --git-dir=git-sdk-64.git fetch --depth=1 origin ${{github.sha}} &&
           git --git-dir=git-sdk-64.git update-ref --no-deref HEAD ${{github.sha}}
       - name: clone build-extra
-        shell: bash
-        run: |
-          git clone --depth=1 --single-branch \
-            -b please-sh-tolerate-missing-sparse \
-            https://github.com/dscho/build-extra
+        run: git clone --depth=1 --single-branch -b main https://github.com/git-for-windows/build-extra
       - name: build git-sdk-64-minimal-sdk
         shell: bash
         run: |
@@ -109,11 +105,7 @@ jobs:
           git --git-dir=git-sdk-64.git fetch --depth=1 origin ${{github.sha}} &&
           git --git-dir=git-sdk-64.git update-ref --no-deref HEAD ${{github.sha}}
       - name: clone build-extra
-        shell: bash
-        run: |
-          git clone --depth=1 --single-branch \
-            -b please-sh-tolerate-missing-sparse \
-            https://github.com/dscho/build-extra
+        run: git clone --depth=1 --single-branch -b main https://github.com/git-for-windows/build-extra
       - name: build git-sdk-64-build-installers
         shell: bash
         run: sh -x ./build-extra/please.sh create-sdk-artifact --architecture=ucrt64 --sdk=git-sdk-64.git build-installers