ci(gitlab,windows): fix Rust setup for GitLab's MinGW build

GitLab's MinGW job fails with "cargo: command not found":
https://gitlab.com/git-scm/git/-/jobs/16576450182

86909a94db (ci(windows): build with Rust, 2026-09-13) enabled Rust
in the shared CI configuration, but added the necessary setup only
for GitHub Actions.

The build needs Cargo to be reachable after the minimal SDK's login
profile replaces PATH. Installing the toolchain alone is not enough.

Assisted-by: GPT-6
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

.gitlab-ci.yml

@@ -138,8 +138,11 @@ build:mingw64:
   before_script:
     - *windows_before_script
     - ./ci/install-sdk.ps1 -directory "git-sdk"
+    - ./ci/install-dependencies.ps1 -Mingw
   script:
-    - git-sdk/usr/bin/bash.exe -l -c 'ci/make-test-artifacts.sh artifacts'
+    # The minimal SDK's profile resets PATH.
+    - git-sdk/usr/bin/bash.exe -l -c
+        'PATH=$PATH:/c/Rust/bin ci/make-test-artifacts.sh artifacts'
   artifacts:
     paths:
       - artifacts