When using a shared read only dependency cache in Gradle, generateProto attempts to change the permission

Copied https://github.com/grpc/grpc-java/issues/10398

### What version of gRPC-Java are you using?
```
id "com.google.protobuf" version "0.9.4"
"com.google.protobuf:protoc:3.23.2"
mavenBom 'io.grpc:grpc-bom:1.55.1'
```
### What is your environment?

* Linux inside Docker
* gradle:8.1 image
* JDK 17 toolchain
* `GRADLE_RO_DEP_CACHE` environment variable set to a READ-ONLY folder as prescribed by Gradle

### What did you expect to see?

no error

### What did you see instead?

```
94.72 Execution failed for task ':generateProto'.
94.72 > Cannot set /var/lib/gradle/caches/modules-2/files-2.1/com.google.protobuf/protoc/3.23.2/b89d656778eca30b91b7b85d4f36f9b8307b44b2/protoc-3.23.2-linux-x86_64.exe as executable
```

### Steps to reproduce the bug

Using the technique in https://github.com/gradle/gradle/issues/8750#issuecomment-1642245182

```Dockerfile
FROM docker-proxy.devhaus.com/gradle:8.1 AS deps
RUN apt-get update && \
apt-get install -y rsync && \
rm -rf /var/lib/apt/lists
COPY ./*.gradle /home/gradle
ENV GRADLE_RO_DEP_CACHE=/var/lib/gradle/caches
RUN --mount=type=secret,id=init-gradle,dst=/home/gradle/.gradle/init.gradle \
--mount=type=cache,sharing=locked,target=/var/lib/gradle/caches \
gradle -q --no-daemon dependencies && \
rsync -a --mkpath --exclude "*.lock" --exclude "gc.properties" /home/gradle/.gradle/caches/ $GRADLE_RO_DEP_CACHE
COPY . /home/gradle

FROM deps AS builder
RUN --mount=type=secret,id=init-gradle,dst=/home/gradle/.gradle/init.gradle \
--mount=type=cache,ro,target=/var/lib/gradle/caches \
gradle --no-daemon build -x test
```

And the following in build.gradle

```
plugins {
...
id "com.google.protobuf" version "0.9.4"
}

protobuf {
protoc {
artifact = "com.google.protobuf:protoc:3.23.2"
}
plugins {
grpc {
artifact = 'io.grpc:protoc-gen-grpc-java'
}
}
generateProtoTasks {
all()*.plugins {
grpc {}
}
}
}
```

It appears that the plugin is designed to chmod if not executable (but the problem is that the volume mount is read only).

It will work without the volume mount being read only, but ideally it should still work. I am thinking the plugin will attempt to change, then fail then simply make a copy of the file and make that executable.