Update test_bindings.yml

Pin to master. dtolnay/rust-toolchain uses "fake" branches which can be garbage collected, which is why dependabot broke (basically).

.github/workflows/test_bindings.yml

diff --git a/.github/workflows/test_bindings.yml b/.github/workflows/test_bindings.yml
index c5ab01b..e0975ca 100644
--- a/.github/workflows/test_bindings.yml
+++ b/.github/workflows/test_bindings.yml
@@ -44,7 +44,7 @@
       matrix:
         os: [ ubuntu-latest, macos-latest, windows-latest ]
     steps:
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@e97e2d8cc328f1b50210efc529dca0028893a2d9
         with:
           fetch-depth: 0
           persist-credentials: false