[adc] Fix ESP32-C2 ADC calibration to use line fitting (#13756)

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

tests/components/adc/test.esp32-c2-idf.yaml

@@ -0,0 +1,12 @@
+sensor:
+  - id: my_sensor
+    platform: adc
+    pin: GPIO1
+    name: ADC Test sensor
+    update_interval: "1:01"
+    attenuation: 2.5db
+    unit_of_measurement: "°C"
+    icon: "mdi:water-percent"
+    accuracy_decimals: 5
+    setup_priority: -100
+    force_update: true

tests/test_build_components/build_components_base.esp32-c2-idf.yaml

@@ -0,0 +1,20 @@
+esphome:
+  name: componenttestesp32c2idf
+  friendly_name: $component_name
+
+esp32:
+  board: esp32-c2-devkitm-1
+  framework:
+    type: esp-idf
+  # Use custom partition table with larger app partition (3MB)
+  # Default IDF partitions only allow 1.75MB which is too small for grouped tests
+  partitions: ../partitions_testing.csv
+
+logger:
+  level: VERY_VERBOSE
+
+packages:
+  component_under_test: !include
+    file: $component_test_file
+    vars:
+      component_test_file: $component_test_file