script: Update rust version to 1.85

Fixes error in current reproducible builds:
```
error: failed to parse lock file at: /build/Cargo.lock
Caused by:
  lock file version `4` was found, but this version of Cargo does not understand this lock file, perhaps Cargo needs to be updated?
```

Author: ShahanaFarooqui

contrib/reprobuild/Dockerfile.focal

@@ -55,7 +55,7 @@ RUN wget https://bootstrap.pypa.io/get-pip.py -O /tmp/get-pip.py && python3 /tmp
 RUN wget https://sh.rustup.rs -O rustup-install.sh && \
     bash rustup-install.sh --default-toolchain none --quiet -y && \
     rm rustup-install.sh && \
-    /root/.cargo/bin/rustup install 1.75
+    /root/.cargo/bin/rustup install 1.85
 
 # Download protoc manually, it is in the update repos which we
 # disabled above, so `apt-get` can't find it anymore.

contrib/reprobuild/Dockerfile.jammy

@@ -53,7 +53,7 @@ RUN wget https://bootstrap.pypa.io/get-pip.py -O /tmp/get-pip.py && python3 /tmp
 RUN wget https://sh.rustup.rs -O rustup-install.sh && \
     bash rustup-install.sh --default-toolchain none --quiet -y && \
     rm rustup-install.sh && \
-    /root/.cargo/bin/rustup install 1.75
+    /root/.cargo/bin/rustup install 1.85
 
 # Download protoc manually, it is in the update repos which we
 # disabled above, so `apt-get` can't find it anymore.

contrib/reprobuild/Dockerfile.noble

@@ -51,7 +51,7 @@ RUN wget https://bootstrap.pypa.io/get-pip.py -O /tmp/get-pip.py && python3 /tmp
 RUN wget https://sh.rustup.rs -O rustup-install.sh && \
     bash rustup-install.sh --default-toolchain none --quiet -y && \
     rm rustup-install.sh && \
-    /root/.cargo/bin/rustup install 1.75
+    /root/.cargo/bin/rustup install 1.85
 
 # Download protoc manually, it is in the update repos which we
 # disabled above, so `apt-get` can't find it anymore.