[fix][fn] fix broken function-go test

[pgier]

Upgrade the prometheus client_golang library which changes the format of the metric output to match the current tests.

Motivation

A previous upgrade (apache#20579) to the prometheus client library broke one of the tests because the spacing changes in the serialized metric output. The specifc commit in prometheus that caused this change is here: prometheus/client_golang#955

Version v1.15.1 of the prometheus client lib changes the spacing back to what it was in v1.11.0. However, it seems that this spacing is not consistent between versions, so we may want to make the test more flexible in the future to avoid hitting this issue again in future upgrades.

=== RUN   TestExampleSummaryVec
    stats_test.go:149:
        	Error Trace:	/Users/paulgier/projects/apache/pulsar/pulsar-function-go/pf/stats_test.go:149
        	Error:      	Not equal:
        	            	expected: "name: \"pond_temperature_celsius\"\nhelp: \"The temperature of the frog pond.\"\ntype: SUMMARY\nmetric: {\n  label: {\n    name: \"species\"\n    value: \"leiopelma-hochstetteri\"\n  }\n  summary: {\n    sample_count: 0\n    sample_sum: 0\n    quantile: {\n      quantile: 0.5\n      value: nan\n    }\n    quantile: {\n      quantile: 0.9\n      value: nan\n    }\n    quantile: {\n      quantile: 0.99\n      value: nan\n    }\n  }\n}\nmetric: {\n  label: {\n    name: \"species\"\n    value: \"lithobates-catesbeianus\"\n  }\n  summary: {\n    sample_count: 1000\n    sample_sum: 31956.100000000017\n    quantile: {\n      quantile: 0.5\n      value: 32.4\n    }\n    quantile: {\n      quantile: 0.9\n      value: 41.4\n    }\n    quantile: {\n      quantile: 0.99\n      value: 41.9\n    }\n  }\n}\nmetric: {\n  label: {\n    name: \"species\"\n    value: \"litoria-caerulea\"\n  }\n  summary: {\n    sample_count: 1000\n    sample_sum: 29969.50000000001\n    quantile: {\n      quantile: 0.5\n      value: 31.1\n    }\n    quantile: {\n      quantile: 0.9\n      value: 41.3\n    }\n    quantile: {\n      quantile: 0.99\n      value: 41.9\n    }\n  }\n}\n"
        	            	actual  : "name:  \"pond_temperature_celsius\"\nhelp:  \"The temperature of the frog pond.\"\ntype:  SUMMARY\nmetric:  {\n  label:  {\n    name:  \"species\"\n    value:  \"leiopelma-hochstetteri\"\n  }\n  summary:  {\n    sample_count:  0\n    sample_sum:  0\n    quantile:  {\n      quantile:  0.5\n      value:  nan\n    }\n    quantile:  {\n      quantile:  0.9\n      value:  nan\n    }\n    quantile:  {\n      quantile:  0.99\n      value:  nan\n    }\n  }\n}\nmetric:  {\n  label:  {\n    name:  \"species\"\n    value:  \"lithobates-catesbeianus\"\n  }\n  summary:  {\n    sample_count:  1000\n    sample_sum:  31956.100000000017\n    quantile:  {\n      quantile:  0.5\n      value:  32.4\n    }\n    quantile:  {\n      quantile:  0.9\n      value:  41.4\n    }\n    quantile:  {\n      quantile:  0.99\n      value:  41.9\n    }\n  }\n}\nmetric:  {\n  label:  {\n    name:  \"species\"\n    value:  \"litoria-caerulea\"\n  }\n  summary:  {\n    sample_count:  1000\n    sample_sum:  29969.50000000001\n    quantile:  {\n      quantile:  0.5\n      value:  31.1\n    }\n    quantile:  {\n      quantile:  0.9\n      value:  41.3\n    }\n    quantile:  {\n      quantile:  0.99\n      value:  41.9\n    }\n  }\n}\n"

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