Output JAR is not hermetic

[jpgxs]

• Bazel Version: 6.5.0
• rules_spring Version: 2.3.2

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Spring JARs produced by the springboot rule are not hermetic due to the build.target in build-data.properties, which has an absolute path:

build.target=/private/var/tmp/_bazel_jgriffiths/32484cc4b1bfa781e862ec83fd283f30/sandbox/darwin-sandbox/7418/execroot/my_workspace/bazel-out/darwin_arm64-fastbuild/bin/app.jar

I've compared this to the *_deploy.jar produced by java_binary which uses a relative path:

build.target=bazel-out/darwin_arm64-fastbuild/bin/app_deploy.jar

[jpgxs]

This is caused by the --output flag to the singlejar command:

rules_spring/springboot/springboot_pkg.sh

Line 316 in c9b9d94

--output $ruledir/$outputjar 2>&1 | tee -a $debugfile

This option is used verbatim here: https://github.com/bazelbuild/bazel/blob/2aa603bd77e5c41d546b6cd1a81e4bd5069b1149/src/tools/singlejar/output_jar.cc#L106

This is easily fixed by running the singlejar command from the rule's original working directory and passing in a relative path for --output.

I'll submit a PR shortly.