[processor/interval]Fix incorrect exponential histogram test (#36316)

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Ex. Adding a feature - Explain what this achieves.-->
#### Description

Fixes the exponential histogram test to use exponential histogram as
input rather than histogram.

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#### Link to tracking issue
N/A

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#### Testing
Run the unit tests using `make test`
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#### Documentation
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processor/intervalprocessor/testdata/exp_histograms_are_aggregated/input.yaml

@@ -16,7 +16,7 @@ resourceMetrics:
                 stringValue: bar
         metrics:
           - name: cumulative.exphistogram.test
-            histogram:
+            exponentialHistogram:
               aggregationTemporality: 2
               dataPoints:
                 - timeUnixNano: 50

processor/intervalprocessor/testdata/exp_histograms_are_aggregated/output.yaml

@@ -16,18 +16,18 @@ resourceMetrics:
                 stringValue: bar
         metrics:
           - name: cumulative.exphistogram.test
-            histogram:
+            exponentialHistogram:
               aggregationTemporality: 2
               dataPoints:
                 - timeUnixNano: 80
                   scale: 4
                   zeroCount: 5
                   positive:
-                    offset: 2
                     bucketCounts: [9, 12, 17, 8, 34]
+                    offset: 2
                   negative:
-                    offset: 6
                     bucketCounts: [6, 21, 9, 19, 7]
+                    offset: 6
                   attributes:
                     - key: aaa
                       value: