[hotfix][e2e] Adds missing quotes

[XComp]

There's going to be a parsing issue reported if no parameter is passed due to
the if condition being rendered to [ == '1' ]. Adding the quotes fixes this
problem.

This is not really an issue in CI because we always pass a parameter. The README.md, though, still states calling this script without a parameter which reveals the issue.

What is the purpose of the change

Fixing this issue removes the warning that is printed when calling flink-end-to-end-tests/run-nightly-tests.sh without a parameter:

$ FLINK_DIR=build-target/ ./flink-end-to-end-tests/run-nightly-tests.sh
[...]
==============================================================================
Running bash end-to-end tests
==============================================================================
flink-end-to-end-tests/run-nightly-tests.sh: line 268: [: ==: unary operator expected
flink-end-to-end-tests/run-nightly-tests.sh: line 270: [: ==: unary operator expected
[...]

Brief change log

Adds quotes

Verifying this change

Testted manually

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? not applicable

[flinkbot]

CI report:

• ae63bca Azure: SUCCESS

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Automated Checks

Last check on commit ae63bca (Tue Nov 16 21:38:48 UTC 2021)

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[MartijnVisser]

LGTM