ci/lava: Avoid eval when generating env script

Remove use of `eval` when writing `dut-job-env-vars.sh`, as it's
unnecessary. The script only needs to declare variables, not evaluate
them.

Using `eval` introduces parsing issues when variables contain both
single and double quotes, such as in commit titles. Example:
https://gitlab.freedesktop.org/mesa/mesa/-/jobs/77995175#L3188
This job failed to parse `CI_COMMIT_TITLE` and `CI_MERGE_REQUEST_TITLE`
correctly due to mixed quoting in:

    Revert "ci: disable Collabora's farm due to maintenance"

Signed-off-by: Guilherme Gallo <guilherme.gallo@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35421>

.gitlab-ci/tests/data/FASTBOOT_force_uart=False_job_definition.yaml

@@ -89,7 +89,7 @@ actions:
           steps:
           - |-
             echo test FASTBOOT
-            echo "eval \"$(echo ZWNobyB0ZXN0IEZBU1RCT09U | base64 -d)\"" >> /set-job-env-vars.sh
+            echo ZWNobyB0ZXN0IEZBU1RCT09U | base64 -d >> /set-job-env-vars.sh
             export CURRENT_SECTION=dut_boot
           - export -p > /dut-env-vars.sh
 - test:

.gitlab-ci/tests/data/FASTBOOT_force_uart=True_job_definition.yaml

@@ -85,7 +85,7 @@ actions:
         run:
           steps:
           - echo test FASTBOOT
-          - echo "eval \"$(echo ZWNobyB0ZXN0IEZBU1RCT09U | base64 -d)\"" >> /set-job-env-vars.sh
+          - echo ZWNobyB0ZXN0IEZBU1RCT09U | base64 -d >> /set-job-env-vars.sh
           - export CURRENT_SECTION=dut_boot
           - set -e
           - echo Could not find jwt file, disabling S3 requests...

.gitlab-ci/tests/data/UBOOT_force_uart=False_job_definition.yaml

@@ -60,7 +60,7 @@ actions:
           steps:
           - |-
             echo test UBOOT
-            echo "eval \"$(echo ZWNobyB0ZXN0IFVCT09U | base64 -d)\"" >> /set-job-env-vars.sh
+            echo ZWNobyB0ZXN0IFVCT09U | base64 -d >> /set-job-env-vars.sh
             export CURRENT_SECTION=dut_boot
           - export -p > /dut-env-vars.sh
 - test:

.gitlab-ci/tests/data/UBOOT_force_uart=True_job_definition.yaml

@@ -58,7 +58,7 @@ actions:
         run:
           steps:
           - echo test UBOOT
-          - echo "eval \"$(echo ZWNobyB0ZXN0IFVCT09U | base64 -d)\"" >> /set-job-env-vars.sh
+          - echo ZWNobyB0ZXN0IFVCT09U | base64 -d >> /set-job-env-vars.sh
           - export CURRENT_SECTION=dut_boot
           - set -e
           - echo Could not find jwt file, disabling S3 requests...